Ages at diagnosis of pheochromocytomas and paragangliomas vary according to the catecholamine phenotypes and locations of tumors.
Abstract
Context:
Pheochromocytomas and paragangliomas (PPGLs) are diagnosed earlier in patients with hereditary than sporadic disease. Whether other factors influence age at diagnosis is unclear.
Objective:
We examined ages at which PPGLs were diagnosed according to different catecholamine phenotypes and locations of tumors.
Design & Setting:
Retrospective multicenter study.
Patients:
Patients with PPGLs included 172 with and 183 without identified germline mutations or hereditary syndromes.
Biochemical Measurements:
Differences in plasma concentrations of metanephrine, a metabolite of epinephrine, were used to distinguish epinephrine-producing tumors from those lacking epinephrine production.
Results:
Patients with epinephrine-producing tumors were diagnosed 11 yr later (P < 0.001) than those with tumors lacking appreciable epinephrine production. Among patients without evidence of a hereditary condition, those with and without epinephrine-producing tumors had respective mean ± se ages of 50 ± 2 and 42 ± 2 yr (P < 0.001) at diagnosis. Patients with multiple endocrine neoplasia type 2 and neurofibromatosis type 1, all with epinephrine-producing tumors, were similarly diagnosed with disease at a later age than patients with tumors that lacked appreciable epinephrine production secondary to mutations of von Hippel-Lindau and succinate dehydrogenase genes (40 ± 2 vs. 31 ± 1 yr, P < 0.001). Among the latter patients, those with multifocal tumors were diagnosed earlier than those with solitary tumors (19 ± 3 vs. 34 ± 2 yr, P < 0.001).
Conclusions:
The variations in ages at diagnosis associated with different tumor catecholamine phenotypes and locations suggest origins of PPGLs from different chromaffin progenitor cells with variable susceptibility to disease causing mutations. Different optimal age cut-offs for mutation testing are indicated for patients with and without epinephrine-producing tumors (44–49 vs. 30–35 yr, respectively).
Pheochromocytomas and paragangliomas (PPGLs) are rare catecholamine-producing tumors, a large proportion of which have a hereditary basis due to germline mutations of several tumor susceptibility genes (1–3). Both hereditary and sporadic PPGLs differ markedly in tumor contents of catecholamines and corresponding plasma and urinary hormonal profiles. About 50% of the tumors produce and contain a mixture of norepinephrine and epinephrine, while most of the rest produce near exclusively norepinephrine, with occasional rare tumors producing mainly dopamine (4).
Because tumoral catecholamine secretion can be highly variable, relative increases in plasma concentrations of norepinephrine and epinephrine provide poor reflections of tumor catecholamine contents (5). In contrast, the O-methylated metabolites, normetanephrine and metanephrine, are produced continuously within tumor cells from catecholamines leaking from storage vesicles. Consequently increases in plasma concentrations of these metabolites above normal show a strong positive relationship with relative amounts of norepinephrine and epinephrine in tumor tissue (5). Thus, differences in tumoral catecholamine production and contents among PPGLs are best assessed by measurements of plasma concentrations of normetanephrine and metanephrine.
Among hereditary PPGLs, those that develop due to mutations of the von Hippel–Lindau (VHL) gene are characterized by increases exclusively of plasma normetanephrine, indicating norepinephrine production (6). In contrast, patients with multiple endocrine neoplasia type 2 (MEN 2) due to mutations of the RET gene develop tumors characterized by additional increases in plasma metanephrine, indicating production of epinephrine (6). These differences are associated with distinct gene expression profiles that parallel similarly distinct profiles among patients with sporadic PPGLs characterized by presence and absence of epinephrine production (7).
Age at which PPGLs are diagnosed represents a consistently observed difference among patients with hereditary and sporadic tumors, with patients in the former group presenting with tumors on average 12–19 yr earlier than those with sporadic disease (1–3). Beyond this it is not clear whether other factors influence or are associated with differences in age at diagnosis in patients with hereditary and sporadic PPGLs. The present analysis therefore used a dataset from a large population of patients with PPGLs to assess whether age at tumor diagnosis might also be associated with differences in catecholamine biochemical phenotypes or locations of tumors.
Subjects and Methods
The study involved retrospective analysis of data from 355 patients with pathologically confirmed PPGLs who were tested for the tumors between 1994 and 2009. The majority of subjects were investigated at the National Institutes of Health (NIH), Bethesda, MD in the United States and the remainder at European Centers, including Radboud University Medical Center at Nijmegen in The Netherlands, the University of Florence in Italy, and the University Hospital at Dresden in Germany. Written informed consent was obtained from patients enrolled into intramural review board approved studies at the NIH. At European centers, when informed consent was not obtained, the data were collected under conditions of regular clinical care, with ethical committee approval obtained for the use of those data for scientific purposes.
Patients with PPGLs had a mean age of 40 yr (range 6 to 83 yr) at initial diagnosis of tumors and included 185 males and 170 females. Adrenal and extraadrenal locations of tumors were determined using results of imaging studies and surgical and pathological records. For patients presenting with recurrent or malignant PPGLs, careful attention was made to assess the adrenal or extraadrenal locations of primary tumors, history or presence of multi-focal disease and ages when initial tumors were first diagnosed.
Patients included 173 with clearly identified hereditary syndromes or gene mutations and 182 in whom there was no clearly identified mutation or evidence of an established hereditary syndrome. The high proportion of patients with hereditary syndromes or gene mutations largely reflects disproportionate referral of those patients to the participating specialist centers. Among the group of 173 patients with hereditary PPGLs, there were 66 with VHL syndrome, 38 with MEN 2, 10 with neurofibromatosis type 1 (NF1), and 59 with mutations of genes for subunits of succinate dehydrogenase (SDH). The latter included 48 patients with mutations of the gene for SDH subunit B (SDHB) and 11 with mutations of the gene for SDHD.
All patients with MEN 2 and NF1 and most with VHL syndrome were diagnosed with already established gene mutations or hereditary syndromes at the time of testing for catecholamine-producing tumors. However, one patient was identified with a VHL gene mutation, 37 were identified with SDHB gene mutations, and 8 with SDHD gene mutations as a consequence of routine testing of RET, VHL, SDHD, and SDHB genes implemented after 2005 in all patients with apparently sporadic PPGLs. Detection of SDHB and SDHD mutations in other patients was based on clinical suspicion of a hereditary paraganglioma syndrome. Among the 182 patients with no evidence of an established hereditary syndrome, gene testing failed to confirm the presence of germline mutations of VHL, RET, SDHD, or SDHB genes in DNA available from 87 patients. DNA from the other 95 patients was not available. The study did not include testing of the more recently described tumor susceptibility genes for SDH subunit A, the SDH complex assembly factor 2, and transmembrane protein 127 (8–10).
PPGLs in most of the patients with MEN 2 and VHL syndrome, as well as one patient with an SDHD mutation, were found as a consequence of routine screening for tumors due to an established hereditary condition. In contrast, clinical suspicion of PPGLs in 10 of the 11 patients with SDHD mutations and all patients with NF1 and SDHB mutations was based on signs and symptoms of catecholamine excess, a finding of an incidental mass during imaging studies for other conditions or clinical findings (e.g., head and neck tumors). Clinical suspicion of PPGLs in patients without evidence of a hereditary syndrome was also based on signs and symptoms or other findings suggesting a catecholamine-producing tumor.
Patients identified with disease-causing mutations or hereditary syndromes were divided into five subgroups (VHL, MEN 2, NF1, SDHB, and SDHD) according to the nature of the syndrome or gene mutation. Patients without evidence of a hereditary syndrome or mutation were divided into two subgroups according to the catecholamine phenotypes of their tumors.
Designation of catecholamine phenotypes was based on previous criteria in which relative tumor-derived increases in plasma concentrations of normetanephrine and metanephrine were determined to accurately reflect relative tumor tissue contents of the two catecholamines (5). All 284 patients in that study focusing on catecholamine phenotyping were also included in the present study. Further refinements to the criteria included additional consideration of plasma concentrations of methoxytyramine, the O-methylated metabolite of dopamine, and use of mean concentrations of metabolites in a reference group to establish tumor-derived increments of metabolites. Tumor-derived increments were calculated by subtracting the concentration of each metabolite in each patient with a PPGL from mean concentrations of normetanephrine (53 pg/ml or 0.29 nmol/liter), metanephrine (26 pg/ml or 0.13 nmol/liter), and methoxytyramine (4 pg/ml or 0.02 nmol/liter) in a previously established reference group (5, 11). The minimum determined value was assigned when there was no increase above the reference group. Epinephrine-producing tumors were defined as those in patients who showed both an increase in plasma metanephrine above the upper reference intervals (61 pg/ml) and a tumor-derived increment of metanephrine larger than 5% of combined increments of all O-methylated metabolites. All other PPGLs were designated as tumors that did not produce appreciable epinephrine.
Blood samples obtained from all patients were processed and assayed for plasma concentrations of free normetanephrine, metanephrine, and methoxytyramine by liquid chromatography with electrochemical detection as described elsewhere (12).
Statistical analysis of differences involving comparisons of multiple groups was by one-way or two-way ANOVA depending on respective absence or presence of more than one independent variable. The Tukey-Kramer test was used for post hoc comparisons among multiple groups. Relationships between age and other variables were assessed by linear regression analysis with significance determined by both parametric (Pearson's tests) and nonparametric methods (Spearman's test). Logistic regression was used to establish receiver-operating characteristic (ROC) curves that related proportions of patients with (sensitivity) and without (specificity) hereditary tumors as a function of age. ROC curves were then used to identify the optimal cut-off values for age as a discriminator of patients with and without hereditary PPGLs.
Results
Designation of catecholamine phenotypes
A scatterplot of plasma concentrations of metanephrine vs. tumor-derived relative increases of plasma metanephrine revealed that all patients with MEN 2 and NF1 had both increased plasma metanephrine and proportional increases of metanephrine above mean reference values that were larger than 5% of the summed total of tumor-derived increases of O-methylated metabolites (Fig. 1A). By the criteria outlined in the methods section, these patients were all designated as having epinephrine-producing tumors. In contrast, all except two patients with mutations of SDH or VHL genes had normal plasma concentrations of metanephrine or tumor-derived increases of plasma metanephrine that were less than 5% the summed increases of metabolites.
Fig. 1.
Characterization of PPGLs with and without appreciable epinephrine production. A, Scatterplot relationship of plasma concentrations of metanephrine vs. increases of plasma metanephrine as a percent of increases of the summed total of all O-methylated metabolites above reference. B, Mean ± sem plasma concentrations of metanephrine (MN) among the different groups of patients with PPGLs. The dashed vertical line in panel A depicts the upper reference limits (61 pg/ml) used to establish increased vs. normal plasma concentrations of metanephrine. The dashed horizontal line in panel A depicts the cut-off at 5% used to establish appreciable metanephrine (epinephrine) production. Among patients without evidence of hereditary disease, tumors showing both increased plasma concentrations of metanephrine (>61 pg/ml) and relative increases of metanephrine above the cut-off (>5%) were designated as those with appreciable epinephrine production (i.e., EPI group in panel B). All others were designated as those without appreciable epinephrine production (i.e., No EPI group in panel B). To convert plasma concentrations of metanephrine to nmol per liter divide by the molecular weight of metanephrine (197.2). *, Lower (P < 0.05) plasma concentrations of metanephrine than in MEN 2 and NF1 groups or the group with no appreciable epinephrine production and no evidence of hereditary disease.
Using the same criteria, 95 of the 182 patients without evidence of hereditary syndrome or mutation were designated as having epinephrine-producing tumors, while the other 87 patients were designated with tumors lacking appreciable epinephrine production. The former patients with epinephrine-producing tumors had plasma concentrations of metanephrine that were similar to concentrations in patients with MEN 2 and NF1 (Fig. 1B). All three groups with epinephrine-producing tumors had plasma concentrations of metanephrine that were more than 10-fold higher (P < 0.001) than concentrations in patients with mutations of SDH and VHL genes or those without evidence of a hereditary syndrome or appreciable epinephrine production.
Age of tumor diagnosis
As a single group, patients with an established mutation or hereditary syndrome had their first presenting tumors diagnosed at a 14-yr earlier age than patients without an established mutation or hereditary syndrome (mean ± sd; 33 ± 15 vs. 47 ± 16 yr; P < 0.0001). Within the groups, however, there was considerable variation in ages of initial diagnosis (Table 1). Patients with tumors due to VHL, SDHB, and SDHD mutations represented the groups with the youngest ages at first diagnosis, all presenting with their first tumors at a mean age of 31 yr. In contrast, patients with tumors associated with MEN 2, NF1, or with no established mutation and without appreciable epinephrine production had their tumors diagnosed at 9- to 11-yr later ages. Patients with epinephrine-producing tumors and with no established mutation represented the group with the highest age at initial diagnosis of disease. Tumors in these patients were diagnosed on average 19 yr later than in patients with VHL, SDHB, and SDHD mutations.
Table 1.
Ages of diagnosis and locations of tumors in patients with and without established mutations or hereditary syndromes
| MEN 2 | Established mutation or hereditary syndrome |
SDHD | No established mutation or hereditary syndrome |
||||
|---|---|---|---|---|---|---|---|
| NF 1 | VHL | SDHB | EPI | No EPI | |||
| No. | 38 | 10 | 66 | 48 | 11 | 95 | 87 |
| Age data | a | ab | ab | a | a | ||
| Mean ± 95% CI | 39.6 ± 4.1 | 42.1 ± 7.9 | 30.6 ± 4.1 | 31.3 ± 4.2 | 30.7 ± 8.8 | 50.4 ± 3.0c | 42.4 ± 3.2 |
| Median | 36.1 | 43.2 | 28.5 | 32.4 | 23.3 | 50.3 | 41.6 |
| Range | (16–75) | (17–59) | (6–75) | (7–70) | (12–59) | (18–78) | (11–83) |
| 10th & 90th percentiles | (27–54) | (26–55) | (10–55) | (11–50) | (20–53) | (31–71) | (24–64) |
| Tumor location (A/E/B) | 38/0/0 | 9/1/0 | 58/5/3 | 2/43/3 | 1/5/5 | 91/4/0 | 54/30/3 |
Patients without an established mutation were divided into two groups according to whether their tumors produced appeciable epinephrine (EPI) or did not produce appreciable epinephrine (no EPI) as outlined in Fig. 1.
Tumor locations indicate adrenal (A), extradrenal (E), or both adrenal and extraadrenal (B) primary tumors.
Denotes a lower age (P < 0.05) than EPI.
Denotes a lower age (P < 0.05) than No EPI.
After separating patients into two groups with (n = 143) and without (n = 212) epinephrine-producing PPGLs, those with epinephrine-producing tumors presented with disease at a later age than those with tumors that produced negligible epinephrine (mean ± sd; 47 ± 15 vs. 36 ± 17 yr; P < 0.0001). This difference retained significance (F = 24.1, P < 0.0001) when examined separately in patients with and without evidence of hereditary disease (Fig. 2A). Furthermore, the difference in ages at diagnosis among the two groups of patients with no evidence of hereditary disease remained significant after exclusion of the patients who were not tested for germline mutations (mean ± sd; 50 ± 14 vs. 42 ± 16; P = 0.015).
Fig. 2.
Bar graphs showing ages of disease presentation in patients with PPGLs. Comparisons between patients with tumors characterized by presence and absence of epinephrine production, according to presence or absence of a hereditary syndrome are shown in panel A. Comparisons between patients with tumors characterized by adrenal and extraadrenal locations (the latter including tumors with combined extraadrenal and adrenal locations) according to presence or absence of a hereditary syndrome are shown in panel B. Comparisons between patients with and without epinephrine-producing tumors according to adrenal vs. extraadrenal locations are shown for patients with hereditary tumors in panel C and for patients without evidence of hereditary disease in panel D. Comparisons between patients with tumors at solitary vs. bilateral adrenal or multifocal extraadrenal and adrenal locations are shown for hereditary tumors according to presence or absence of epinephrine production in panel E. Further stratification of patients with hereditary tumors lacking production of epinephrine (i.e., patients with tumors due to VHL, SDHB, and SDHD gene mutations) into groups with solitary adrenal or extraadrenal tumors compared with bilateral adrenal tumors and multifocal extraadrenal or combined adrenal and extraadrenal tumors is shown in panel F. Presence of different symbols (*†§) indicate significant differences (P < 0.05) between groups, while presence of identical symbols indicates lack of a significant difference.
Patients with epinephrine-producing tumors and no evidence of hereditary disease also presented with tumors at a later (P < 0.05) age than each of the two groups with hereditary PPGLs that did and did not produce epinephrine (Fig. 2A). Patients without hereditary disease and with tumors that did not produce epinephrine also presented with disease at a later (P < 0.05) age than patients with hereditary tumors that did not produce epinephrine (i.e., patients with VHL, SDHB, and SDHD mutations). Those particular patients without a hereditary syndrome did not, however, present with disease at a later age than patients with hereditary epinephrine-producing tumors (i.e., patients with MEN 2 and NF1).
Adrenal tumors were also diagnosed at a later age than extraadrenal tumors (mean ± sd; 43 ± 17 vs. 35 ± 16 yr; P = 0.002), but this difference did not retain significance when examined separately in patients with or without established disease-causing mutations (Fig. 2B). Furthermore, ages at first diagnosis of PPGLs in patients with adrenal and extraadrenal tumors that produced negligible epinephrine did not differ, irrespective of the presence or absence of hereditary disease (Fig. 2, C and D). Among groups of patients with and without hereditary disease, epinephrine-producing adrenal tumors were, however, diagnosed at later (P < 0.05) ages than both adrenal and extraadrenal tumors that did not produce appreciable epinephrine. Thus, the higher age at diagnosis for patients with tumors that produced epinephrine compared with those that did not produce epinephrine was independent of hereditary factors and tumor location. In contrast, the higher age at diagnosis of patients with adrenal than extraadrenal tumors reflected entirely the predominance of epinephrine-producing tumors at adrenal (54% adrenergic) compared with extraadrenal (5% adrenergic) locations.
Other associations of tumor location with age at first diagnosis emerged when the presence of solitary vs. multifocal or bilateral adrenal tumors was considered among patients with hereditary PPGLs characterized by presence or absence of epinephrine production (Fig. 2, E and F). All tumors in patients with NF1 and MEN 2 were characterized by epinephrine production, and almost all were localized to the adrenals (Table 1). Fifteen of the 48 (31%) patients with NF1 and MEN 2 had bilateral adrenal tumors, but there was no difference in ages at diagnosis among these patients compared with those with solitary adrenal tumors (Fig. 2E). In contrast, among the 125 patients with VHL, SDHB, and SDHD mutations, who had tumors that lacked appreciable epinephrine production, the 87 patients with solitary adrenal or extraadrenal tumors had a higher (P = 0.0013) age at diagnosis than the group of 38 patients with bilateral adrenal tumors, combined adrenal and extra-adrenal tumors, or multifocal extraadrenal tumors.
The difference in ages at diagnosis among patients with hereditary tumors that lacked epinephrine production (i.e., patients with VHL, SDHD, and SDHB mutations) became even more pronounced after patients were partitioned according to presence of solitary adrenal or extraadrenal tumors compared with bilateral adrenal tumors or with multifocal extraadrenal or adrenal and extraadrenal tumors (Fig. 2F). In the latter group, the mean age at diagnosis was only 19 yr compared with 28 yr for patients with bilateral adrenal tumors and 34 yr for patients with solitary adrenal or extraadrenal tumors.
Age-related cut-offs for genetic testing
Ages at which PPGLs were diagnosed showed positive relationships (P < 0.0001) with both plasma concentrations of metanephrine and increases in plasma metanephrine as a percent of the summed total of O-methylated metabolites (Fig. 3). Considerable scatter around regression lines precluded use of these relationships for establishing age-related cut-offs for predicting different hereditary tumor groups. Instead, age-related cut-offs were established by analysis of ROC curves in which age-related variations in proportions of patients with hereditary PPGLs were plotted against age-related variations in proportions of patients with PPGLs and no evident hereditary condition (Fig. 4).
Fig. 3.
Scatterplots relating age of tumor diagnosis to plasma concentrations of metanephrine (A) and increases in plasma metanephrine as a percent of increases in combined O-methylated metabolites (B). To convert plasma concentrations of metanephrine to nmol/liter, divide by the molecular weight of metanephrine (197.2).
Fig. 4.
ROC curve–based determination of optimal age cut-offs for genetic testing. For this analysis, sensitivity was calculated as the number of patients with hereditary PPGLs below a specific age cut-off divided by the total number of patients with hereditary tumors (i.e., percent of patients with hereditary PPGLs in whom mutations would be detected by genetic testing at that age cut-off). Specificity was calculated as the number of patients without hereditary PPGLs above a specific age cut-off divided by the total number of patients without hereditary PPGLs (i.e., percent of patients without hereditary PPGLs in whom testing would not be carried out above that age cut-off). Points of ROC curves (A–C) closest to top left corners indicate optimal values for both sensitivity and specificity. Those optimal values for sensitivity and specificity were then used to identify optimal age cut-offs from relationships of age of diagnosis with proportions of patients with (detected) and without (tested) hereditary tumors (D–F). Areas under ROC curves are 0.722 (A), 0.703 (B), and 0.700 (C).
For combined groups (Fig. 4, A and D), this analysis indicated optimal cut-offs of 35–40 yr; genetic testing in patients <40 yr would only be required in 31% of patents with apparently sporadic disease to reveal 66% of patients with mutations. In contrast, the ROC curve analysis revealed lower optimal cut-offs (30–35 yr) for patients with tumors that did not produce epinephrine (Fig. 4, B and E) and higher cut-offs (44–49 yr) for patients with epinephrine-producing tumors (Fig. 4, C and F).
Discussion
This study involving a large cohort of well-characterized patients with PPGLs outlines novel findings establishing that age at diagnosis varies according to tumor catecholamine phenotype. Furthermore, among patients with hereditary PPGLs that lack epinephrine production, those with multifocal tumors were diagnosed with disease earlier than those with solitary tumors. These findings extend previous observations about lower ages at diagnosis among patients with hereditary than sporadic PPGLs, provide useful information for managing affected patients, and offer unique insight into the underlying biology of chromaffin cell tumors.
The earlier age at diagnosis in hereditary than sporadic PPGLs is an established and expected finding (1–3), whereas the later age in patients with tumors that produce epinephrine compared with those that do not is entirely novel. Nevertheless, there are some hints for this relationship from previous studies about ages at diagnosis among patients with hereditary PPGLs (1–3, 13–17). Analysis of these studies indicates lower overall ages at diagnosis of tumors among patients with VHL, SDHB, and SDHD mutations compared with those with MEN 2 and NF1 (Table 2), findings in good agreement with those here. The single most important additional observation of the present study is that the differences in ages at diagnosis among patients with hereditary PPGLs are associated with differences in catecholamine phenotypes of tumors, an association that extends to patients without evidence of hereditary disease.
Table 2.
Analysis of age at diagnosis of hereditary and sporadic PPGLs from data in eight studies
| MEN 2 |
NF 1 |
VHL |
SDHB |
SDHD |
Sporadic |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Age | n | Age | n | Age | n | Age | n | Age | n | Age | n | |
| Neumann et al., 2002 (1) | 36 | 13 | n.d. | n.d. | 18 | 30 | 26 | 12 | 29 | 11 | 44 | 205 |
| Amar et al., 2005 (2) | 30 | 16 | 40 | 13 | 24 | 25 | 34 | 21 | 31 | 11 | 46 | 228 |
| Mannelli et al., 2009 (3) | 37 | 27 | 42 | 5 | 30 | 48 | 29 | 24 | 40 | 47 | 50 | 340 |
| Cascon et al., 2009 (13) | 39 | 36 | n.d. | n.d. | 28 | 20 | 30 | 25 | 25 | 11 | 46 | 143 |
| Walther et al., 1999 (14) | n.d. | n.d. | 42 | 148 | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. |
| Casanova et al., 1993 (15) | 38 | 100 | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. |
| Pomares et al., 1998 (16) | 38 | 23 | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | 47 | 23 |
| Ricketts et al., 2010 (17) | n.d. | n.d. | n.d. | n.d. | n.d. | n.d. | 27 | 153 | 21 | 18 | n.d. | n.d. |
| Grouped mean & total n | 37 | 215 | 42 | 203 | 26 | 123 | 28 | 235 | 32 | 98 | 47 | 939 |
n.d., No data presented on this group in the study.
What is the basis for the later ages at diagnosis of epinephrine-producing tumors than those that do not produce appreciable epinephrine? The most obvious explanation is that differences in signs and symptoms related to the different catecholamine phenotypes could lead to earlier clinical suspicion of tumors in one group compared with the other. Previous comparisons of patients with PPGLs associated with MEN 2 compared with VHL syndrome indicated, however, that the former patients had a more paroxysmal presentation and were more symptomatic than VHL patients (6). This does not support the possibility that differences in the presentation of signs and symptoms are responsible for the different ages at diagnosis of PPGLs.
While periodic screening for tumors in patients with established disease-causing mutations or syndromes might contribute to the younger age at diagnosis of PPGLs in patients with hereditary compared with sporadic disease, this does not appear to be the most important factor. As shown by studies involving screening for disease-causing mutations in patients with nonsyndromic PPGLs, a younger age at diagnosis is maintained in the patients in whom mutations are identified compared with those without identified mutations (1–3). Thus, it is the presence of germline mutations, not simply tumor screening programs, which results in an earlier age of tumor diagnosis among patients with than without the mutations.
Other evidence indicates that PPGL tumorigenic processes involve arrested differentiation and failure of neuronal apoptosis of chromaffin progenitor cells during embryonic development (18–21). This increasingly popular hypothesis is not only relevant to the earlier ages at diagnosis of hereditary than sporadic PPGLs but is also supported by the present findings which may be explained by origins of different groups of tumors at different stages of chromaffin cell development. This explanation recognizes that the distinguishing characteristics of epinephrine-producing chromaffin cells develop relatively late in embryogenesis, after neural crest chromaffin progenitors have migrated into the adrenal anlagen and then only after induction of phenylethanolamine N-methyltransferase by steroids produced locally by surrounding cortical cells (22, 23). Thus, tumorigenic processes associated with failure of apoptosis in chromaffin progenitors lacking epinephrine production and in which further differentiation is arrested would have to be initiated relatively early in embryogenesis. In contrast, tumorigenic processes in fully differentiated epinephrine-producing chromaffin cells would be expected to occur later or after birth. This in turn would be expected to lead to earlier onset of disease for tumors developing from the former embryonic chromaffin progenitor cells than from the latter fully differentiated epinephrine-producing cells of the adrenal medulla.
The above proposal is further supported by our additional novel findings that among the youngest presenting patients with PPGLs due to VHL and SDH gene mutations, there were further differences in ages at diagnosis depending on locations of tumors. The much earlier ages at diagnosis in patients with multifocal tumors than in patients with solitary PPGLs might be explained by origins of multifocal tumors from single tumor stem cells. In this scenario, which builds on the Knudson two-hit hypothesis (24), the second chromosomal “hit” in some patients with VHL or SDH-associated tumors would occur during migration of embryonic neural crest cells to different paraganglial or adrenal locations. Such second hits occurring during embryogenesis would be expected to result in an earlier onset of disease than those normally occurring later in life. As the affected tumor stem cell migrates and divides, such second “hits” can also be expected to lead to multiple tumors at different locations. Lack of differences in ages at diagnosis among patients with epinephrine-producing bilateral compared with solitary tumors is expected because in those patients any further genetic abnormalities leading to tumorigenesis could only be expected after chromaffin progenitors have migrated and differentiated into epinephrine-producing chromaffin cells within each adrenal.
Current recommendations about whether patients with apparently sporadic PPGLs should be tested for disease-causing mutations cite an early age at diagnosis as one of the most important factors to consider when deciding on mutation testing (25–28). Ages of anything between 35 to 50 yr have been cited as providing cut-offs beyond which mutation testing is of little benefit. Our analysis of ROC curves indicates an optimal maximum cut-off of 40 yr. More importantly, the analysis indicates lower optimal cut-offs of 30 to 35 yr for testing VHL and SDH mutations in patients with tumors that do not produce increases in plasma metanephrine and higher cut-offs of 44 to 49 yr for testing RET mutations in patients with tumors associated with increases in plasma metanephrine.
Also important for patient management, our findings indicate that children or young adults (<25 yr) with PPGLs due to VHL, SDHB, or SDHD gene mutations have a higher risk for multifocal disease or further tumors than patients with the same mutations who present with PPGLs at a later age. For these younger patients it seems particularly important to ensure no other tumors are missed and that further routine screening on follow-up is thorough and comprehensive.
In summary, the variations in ages at diagnosis associated with different tumor catecholamine phenotypes, underlying germline mutations and tumor locations not only provide potential insight into the developmental origins of chromaffin cell tumors but also indicate useful information for patient management.
Acknowledgments
We thank Thanh-Truc Huynh, Nan Qin, Karen Adams, Stephanie Fliedner, and Tamara Prodanov for technical help or assistance with collections of patient materials and data.
This work was supported by the intramural programs of the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the Center for Cancer Research, National Cancer Institute, at the National Institutes of Health, Bethesda, Maryland and the Deutsche Forschungsgesellschaft.
Disclosure Summary: The authors have nothing to declare.
Footnotes
- MEN 2
- Multiple endocrine neoplasia type 2
- NF1
- neurofibromatosis type 1
- PPGLs
- pheochromocytomas and paragangliomas
- ROC
- receiver-operating characteristic
- SDH
- succinate dehydrogenase
- SDHB
- SDH subunit B
- VHL
- von Hippel-Lindau.
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