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. Author manuscript; available in PMC: 2017 Dec 14.
Published in final edited form as: Cancer Causes Control. 2014 May 17;25(8):959–968. doi: 10.1007/s10552-014-0395-1

Racial/ethnic differences in breast cancer survival by inflammatory histology and hormonal receptor status: An analysis of the Surveillance, Epidemiology, and End Results data

Jill K Schinkel 1, Shelia Hoar Zahm 2, Ismail Jatoi 3, Katherine A McGlynn 2, Christopher Gallagher 1, Catherine Schairer 2, Craig D Shriver 1,4,5, Kangmin Zhu 1,5,*
PMCID: PMC5729913  NIHMSID: NIHMS924465  PMID: 24839049

Abstract

Background

Compared to non-inflammatory breast cancer (non-IBC), inflammatory breast cancer (IBC) has less favorable survival and is more likely to be estrogen receptor (ER) and progesterone receptor (PR) negative. ER+/PR+ tumors, regardless of histology, have less favorable survival. While black women are more likely to have IBC and ER+/PR+ tumors than white women, it is unclear whether the racial disparity in survival is explained by these factors. The objective of this study was to assess racial/ethnic differences in breast cancer survival by inflammatory histology and hormone receptor status.

Methods

This study examined breast cancer mortality among non-Hispanic white (NHW), Hispanic white (HW), black, and Asian/Pacific Islander (API) women diagnosed between 1990 and 2004. Kaplan-Meier survival curves and Cox proportional hazard ratios (HRs) assessed the relationship between race/ethnicity and survival.

Results

Black women had significantly poorer survival than NHW women regardless of inflammatory histology and hormone receptor status. Compared to NHWs, the HRs for black women were 1.32 (95% CI 1.21–1.44), 1.43 (95% CI 1.20–1.69) and 1.30 (95% CI 1.16–1.47) for IBC, IBC with ER+/PR+, and with ER−/PR−, respectively. Similar HRs were found for non-IBC, non-IBC with ER+/PR=, and non-IBC with ER−/PR−. API women had significantly better survival than NHW women regardless of inflammatory histology and hormone receptor status.

Conclusion

Compared to NHW women, black women had poorer survival regardless of inflammatory status and hormone receptor status and API women had better survival. These results suggest that factors other than histology and hormone receptor status may play a role in racial/ethnic disparities in breast cancer survival.

Keywords: Breast cancer, Hormone receptor, Inflammatory, Race, SEER, Survival

Background

It is well known that black patients have significantly shorter survival from breast cancer compared to white patients (1). Part of the racial disparity may be related to racial differences in inflammatory histology and hormone-receptor status of the disease. Inflammatory breast cancer (IBC) is an uncommon type of breast cancer that is notably more aggressive and has less favorable survival outcomes compared to non-inflammatory breast cancer (non-IBC). Patients with IBC have a 43% higher rate of death than those with non-IBC after adjusting for factors related to prognosis (2). While it is known that overall breast cancer mortality rates for black women are 39% greater than that for white women (1), studies showed that black women are more likely to be diagnosed with IBC compared to white women (3). Nevertheless, within IBC, black women had a shorter median survival time (20 months) than their white counterparts (32 months) (3, 4).

Hormone receptor status (estrogen receptor, ER, and progesterone receptor, PR) is well known to be an independent predictor of breast cancer survival (5–9): breast cancer patients with hormone receptor negative tumors have increased mortality and shorter survival compared to those with hormone receptor positive tumors. It is well known that black women are nearly twice as likely to have ER and PR negative tumors compared to white women (5, 10–12). While the higher rates of hormone receptor negative tumors among black women may account for some of the black-white disparity in survival (5), other factors must also be important because this disparity persists after accounting for hormone receptor status (13).

Inflammatory histology and hormone receptor status of breast cancer may be related. IBC patients are more likely to have ER/PR negative tumors (11, 14). In addition, IBC survival may be worse if tumors are also hormone-receptor negative (14). Because black patients are more likely to have both IBC and ER+/PR+ tumors than white patients, it would be important to know whether the black/white difference in IBC survival is explained at least partially by more ER+/PR+ tumors among blacks and whether the black/white disparity in IBC survival is greater among patients with tumors that are also ER- and PR-. To the best of our knowledge, there have been no studies that have assessed black/white differences in breast cancer survival by both inflammatory histology and hormone receptor status of the disease. Furthermore, no other racial/ethnic groups have been compared with non-Hispanic whites for breast cancer survival by both histology and hormone receptor status. The objective of this study was to assess if blacks, non-Hispanic whites (NHWs), Hispanic whites (HWs) and Asian/Pacific Islanders (APIs) differ in breast cancer survival by both inflammatory histology and hormone receptor status using the National Cancer Institute’s Surveillance Epidemiology, and End Results (SEER) data.

Methods

Data source and study subjects

This study was based on the National Cancer Institute’s SEER database for public use that consists of eighteen population-based registries (SEER-18, November 2011 Submission) (15). The SEER program has collected cancer registry data since 1973 and had data available through 2009 at the time of this study. The eighteen registries included San Francisco-Oakland (1973–2009), Connecticut (1973–2009), Metropolitan Detroit (1973–2009), Hawaii (1973–2009), Iowa (1973–2009), New Mexico (1973–2009), Seattle-Puget Sound (1974–2009), Utah (1973–2009), Metropolitan Atlanta (1975–2009), San Jose-Monterey (1992–2009), Los Angeles (1992–2009), rural Georgia (1992–2009), greater California-excluding San Francisco Los Angeles & San Jose (2000–2009), Kentucky (2000–2009), Louisiana (2000–2009, except July – December 2005), New Jersey (2000–2009), greater Georgia-excluding Atlanta and Rural Georgia (2000–2009), and Alaska (1992–2009) (15), which represent approximately 28% of the United States population (16). Since the Alaska Native Registry only collects data on American Indian and Alaska Native populations, it was excluded from the study.

The subjects of this study were women aged 18 or older who were histologically diagnosed with breast cancer. Data on ER and PR became available in 1990; therefore, only patients diagnosed from 1990 to 2009 were included. Racial/ethnic groups included in the study were NHWs, HWs, blacks, and APIs. All black and API women were eligible for inclusion regardless of ethnicity. Other races were excluded due to insufficient sample size. As IBC is always diagnosed at least as stage IIIB breast cancer due to involvement of the dermal lymphatics (17), only women with American Joint Committee on Cancer (AJCC) stages IIIB, IIIC or IV were included.

Study variables

The study subjects were classified by whether their cancer was inflammatory or non-inflammatory, as well as by hormone receptor status. IBC cases were defined using the comprehensive case definition which includes: histologic type ICD-O-3 equaling to ‘8530’ (18), historic extent of disease equaling to 70 for years 1990 to 2003, or derived AJCC extent of the tumor (T, 6th edition) equaling to ‘T4d’ and collaborative staging extension being between 71 and 73 for years 2004 and later (19–21). Hormone receptors included ER and PR. The positive and negative states of ER or PR were determined by tumor specimen assay results prior to receipt of neoadjuvant systemic therapy (if available) or after systemic treatment (otherwise). If any sample was recorded as receptor positive, then the receptor was documented as positive (22). Based on the states of ER and PR, there were three mutually exclusive hormone receptor groups. Tumors that were positive for both estrogen and progesterone receptors were categorized as hormone receptor positive (ER+/PR+), and tumors that were negative for both receptors were grouped as hormone receptor negative (ER+/PR+). If estrogen or progesterone receptor states did not coincide, hormonal status was defined as being mixed (ER+/PR- or ER-/PR+). Cases not belonging to any of the three ER/PR groups were excluded from the analysis.

Vital status was determined as of December 31, 2009. Cause of death was obtained from the SEER cause-specific death classification, which is supplied by cancer registries based on the underlying cause of death from death certificates. The outcome for this study was death of breast cancer. Women who died of causes other than breast cancer were censored.

Statistical Analyses

We first described the distribution of demographic, pathologic, and tumor characteristics by race/ethnicity and inflammatory status. We then conducted survival analysis. Breast cancer-specific survival time in years was defined as time from diagnosis date until death date, last contact date, or study cutoff date (December 31, 2009) if still alive.

We used the Kaplan-Meier method to estimate breast cancer-specific survival time by race/ethnicity and the log-rank statistic to evaluate if there were statistical differences between racial/ethnic groups within each subgroup defined by inflammatory status or/and hormone receptor status.

For each of the subgroups stratified by inflammatory status or/and hormone receptor status, the Cox proportional hazard regression analysis was used to assess racial/ethnic differences while adjusting for potential confounders including age at diagnosis, marital status, stage, grade, surgery, and radiation. The hazard ratios (HRs) and their 95% confidence intervals (CIs) were calculated. To evaluate if racial/ethnic differences might vary by menopausal status of the patients, we further conducted Cox analysis stratified by age (<50 vs. >=50 years, a surrogate of menopausal status). The assumptions of the proportional hazards model were confirmed by visual assessment of the residuals. A two-sided p-value of ≤ 0.05 was used to determine statistical significance. SAS 9.3 (SAS Institute, Inc., Cary, NC) was utilized for all analyses.

Results

The study subjects were 30,258 NHW, 6,448 black, 4,183 HW, and 2,691 API female breast cancer patients, including 7,748 (18%) diagnosed with IBC and 35,832 (82%) with non-IBC (Table 1). For both IBC and non-IBC, HWs, APIs, and blacks tended to be younger compared to NHWs. Compared to other racial/ethnic groups, black patients were less likely to be married, undergo surgery and radiation treatment for both IBC and non-IBC. Inflammatory breast tumors were more likely to be ER+/PR+ for all racial/ethnic groups. Despite inflammatory status, blacks were more likely to have ER+/PR+ tumors than women in the other racial/ethnic groups. NHWs tended to be less likely to have stage IV IBC or grade III/IV non-IBC than minority groups.

Table 1.

Demographic, tumor, and treatment characteristics by race/ethnicity and histology among breast cancer patients, SEER 18, 1990–2009

Non-inflammatory breast cancer Inflammatory breast cancer
Characteristic NH
White		 No. of
patients
%		 Black No. of
patients
%		 Hispanic
White		 No. of
patients
%		 API No. of
patients
%		 NH
White		 No. of
patients
%		 Black No. of
patients
%		 Hispanic
White		 No. of
patients
%		 API No. of
patients
%
Age at diagnosis
 18–44 2,603 10.4% 965 18.2% 795 24.0% 414 17.9% 816 15.3% 299 25.8% 263 30.1% 98 25.7%
 45–54 5,030 20.2% 1,293 24.5% 855 25.8% 623 27.0% 1,390 26.1% 336 29.0% 280 32.0% 111 29.1%
 55–64 5,835 23.4% 1,314 24.8% 720 21.8% 589 25.5% 1,420 26.6% 238 20.5% 160 18.3% 97 25.4%
 65–74 5,197 20.8% 922 17.4% 515 15.6% 380 16.5% 865 16.2% 167 14.4% 101 11.6% 48 12.6%
 75+ 6,261 25.1% 794 15.0% 424 12.8% 303 13.1% 841 15.8% 120 10.3% 70 8.0% 28 7.3%
Marital status
 Married 12,019 48.2% 1,569 29.7% 1,641 49.6% 1,307 56.6% 2,870 53.8% 377 32.5% 461 52.7% 230 60.2%
 Never married 3,287 13.2% 1,697 32.1% 662 20.0% 384 16.6% 683 12.8% 347 29.9% 201 23.0% 74 19.4%
 Other 8,753 35.1% 1,825 34.5% 876 26.5% 558 24.2% 1,607 30.1% 385 33.2% 189 21.6% 72 18.8%
 Unknown 867 3.5% 197 3.7% 130 3.9% 60 2.6% 172 3.2% 51 4.4% 23 2.6% 6 1.6%
Stage
 Stage III 10,942 43.9% 2,363 44.7% 1,654 50.0% 1,113 48.2% 4,270 80.1% 822 70.9% 668 76.4% 278 72.8%
 Stage IV 13,984 56.1% 2,925 55.3% 1,655 50.0% 1,196 51.8% 1,062 19.9% 338 29.1% 206 23.6% 104 27.2%
Tumor Grade
 Grade I 1,500 6.0% 203 3.8% 170 5.1% 119 5.2% 111 2.1% 11 0.9% 16 1.8% 6 1.6%
 Grade II 7,870 31.6% 1,247 23.6% 971 29.3% 650 28.2% 1,180 22.1% 203 17.5% 199 22.8% 76 19.9%
 Grade III 10,945 43.9% 2,944 55.7% 1,691 51.1% 1,193 51.7% 3,039 57.0% 707 60.9% 511 58.5% 238 62.3%
 Grade IV 567 2.3% 138 2.6% 100 3.0% 52 2.3% 216 4.1% 50 4.3% 38 4.3% 17 4.5%
 Unknown 4,044 16.2% 756 14.3% 377 11.4% 295 12.8% 786 14.7% 189 16.3% 110 12.6% 45 11.8%
Surgery at BC site
 Yes 17,190 69.0% 3,431 64.9% 2,413 72.9% 1,649 71.4% 4,339 81.4% 824 71.0% 710 81.2% 296 77.5%
 No 7,666 30.8% 1,839 34.8% 892 27.0% 651 28.2% 977 18.3% 332 28.6% 163 18.6% 84 22.0%
 Unknown 70 0.3% 18 0.3% 4 0.1% 9 0.4% 16 0.3% 4 0.3% 1 0.1% 2 0.5%
Radiation
 Yes 10,912 43.8% 2,169 41.0% 1,436 43.4% 1,108 48.0% 2,958 55.5% 547 47.2% 434 49.7% 200 52.4%
 No 13,242 53.1% 2,936 55.5% 1,768 53.4% 1,140 49.4% 2,155 40.4% 565 48.7% 392 44.9% 166 43.5%
 Unknown 772 3.1% 183 3.5% 105 3.2% 61 2.6% 219 4.1% 48 4.1% 48 5.5% 16 4.2%
Hormone receptor status
 ER and PR+ 14,270 57.2% 2,234 42.2% 1,753 53.0% 1,213 52.5% 2,101 39.4% 341 29.4% 322 36.8% 140 36.6%
 ER and PR− 6,207 24.9% 2,105 39.8% 1,001 30.3% 702 30.4% 2,284 42.8% 609 52.5% 389 44.5% 181 47.4%
 ER+/PR− or ER−/PR+ 4,449 17.8% 949 17.9% 555 16.8% 394 17.1% 947 17.8% 210 18.1% 163 18.6% 61 16.0%
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NH=Non-Hispanic, API=Asian/Pacific Islander

The log-rank statistic showed that there were racial/ethnic differences for each of the Kaplan-Meier curves by hormone receptor and inflammatory status (see Figures 1–2). Specifically, for all of the subgroup comparisons, black women tended to have shorter survival than women in other racial/ethnic groups despite inflammatory status or hormone receptor status. A similar racial difference was observed when data were stratified by both inflammatory status and hormone receptor status (data not shown). API women tended to have the longest survival, except for IBC as a whole or IBC with ER/PR both being negative or positive.

Figure 1.

Figure 1

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Kaplan-Meier survival curves by race/ethnicity for non-inflammatory and inflammatory breast cancers, SEER 18, 1990–2009.

Figure 2.

Figure 2

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Kaplan-Meier survival curves by race/ethnicity for ER+/PR+ or ER+/PR+ hormone receptor states, SEER 18, 1990–2009.

Table 2 shows the HRs of minority groups compared to NHWs adjusted for potential confounders. Blacks tended to have significantly increased hazard compared to NHWs despite inflammatory histology or/and hormone receptor status. The adjusted HRs were 1.32 (95% CI 1.21–1.44), 1.43 (95% CI 1.20–1.69), and 1.30 (95% CI 1.16–1.47) for IBC, IBC with ER+/PR+, and IBC with ER+/PR+, respectively. The HRs were similar for non-IBC, non-IBC with ER+/PR+, and non-IBC with ER+/PR+. When ER/PR states were mixed, the results remain similar (data not shown). API women tended to have a lower hazard than NHWs for all ER/PR states and most combinations of ER/PR and inflammatory states. While the HRs tended to be slightly lower than one for HWs compared to NHWs, the differences were never statistically significant.

Table 2.

Cox proportional hazard ratios by inflammatory status and ER/PR states among breast cancer patients, SEER 18, 1990–2009

Strata Race No. of patients No. of deaths Adjusted HRa 95% Confidence intervals
1. Non-IBC
NH White 24,926 11,510 1.00 Reference
Black 5,288 2,716 1.21 1.16 1.27
Hispanic White 3,309 1,313 0.97 0.92 1.03
API 2,309 873 0.87 0.81 0.93
2.IBC
NH White 5,332 2,623 1.00 Reference
Black 1,160 684 1.32 1.21 1.44
Hispanic White 874 404 0.99 0.89 1.11
API 382 171 0.84 0.72 0.98
3.ER+/PR+
NH White 16,371 6,638 1.00 Reference
Black 2,575 1,193 1.32 1.24 1.41
Hispanic White 2,075 717 0.98 0.91 1.06
API 1,353 432 0.88 0.79 0.97
4. ER−/PR−
NH White 8,491 4,757 1.00 Reference
Black 2,714 1,591 1.17 1.11 1.24
Hispanic White 1,390 688 0.97 0.90 1.06
API 883 413 0.85 0.77 0.94
5. Non-IBC and ER+/PR+
NH White 14,270 5,807 1.00 Reference
Black 2,234 1,023 1.32 1.23 1.41
Hispanic White 1,753 595 0.97 0.89 1.06
API 1,213 372 0.84 0.76 0.94
6. IBC and ER+/PR+
NH White 2,101 831 1.00 Reference
Black 341 170 1.43 1.20 1.69
Hispanic White 322 122 1.07 0.88 1.30
API 140 60 1.24 0.95 1.61
7. Non-IBC and ER−/PR−
NH White 6,207 3,445 1.00 Reference
Black 2,105 1,197 1.14 1.07 1.23
Hispanic White 1,001 481 0.98 0.89 1.08
API 702 320 0.87 0.77 0.97
8. IBC and ER−/PR−
NH White 2,284 1,312 1.00 Reference
Black 609 394 1.30 1.16 1.47
Hispanic White 389 207 0.96 0.83 1.12
API 181 93 0.82 0.66 1.01
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a

HR Hazard ratio, adjusted for: age at diagnosis, marital status, stage, grade, surgery, radiation, ER/PR status, and IBC status. The stratified variables were not included in stratified models.

IBC=Inflammatory breast cancer, NH=Non-Hispanic, API=Asian/Pacific Islander

Table 3 shows the adjusted HRs stratified by age at diagnosis. The results among patients aged 50 or older were similar to those in Table 2 except that the HR became no longer significant for APIs with IBC as a whole. Among patients aged younger than 50 years, the HRs for blacks compared to NHWs were higher than the corresponding estimates in the older group for ER+/PR+ or non-IBC with ER+/PR+. The same tendency was observed for non-IBC, and IBC with ER+/PR+. For APIs, the HRs were no longer significantly lower in the younger group. The HRs for younger HWs compared to NHWs were similar to those from the older group. Racial differences in the strata with mixed ER/PR states tended to be similar (data not shown).

Table 3.

Cox proportional hazard ratios by inflammatory status, ER/PR states, and age at diagnosis among breast cancer patients, SEER 18, 1990–2009

Age at diagnosis < 50 Age at diagnosis ≥ 50
Strata Race No. of patients No. of deaths Adjusted HRa 95% Confidence intervals No. of patients No. of deaths Adjusted HRa 95% Confidence intervals
1. Non-IBC
NH White 4,875 1,962 1.00 Reference 20,051 9,548 1.00 Reference
Black 1,561 776 1.33 1.21 1.45 3,727 1,940 1.18 1.12 1.24
Hispanic White 1,211 420 1.00 0.90 1.11 2,098 893 0.96 0.90 1.03
API 711 262 1.03 0.91 1.18 1,598 611 0.83 0.76 0.90
2.IBC
NH White 1,455 702 1.00 Reference 3,877 1,921 1.00 Reference
Black 455 270 1.38 1.19 1.59 705 414 1.28 1.14 1.42
Hispanic White 392 182 0.98 0.83 1.15 482 222 0.99 0.86 1.14
API 139 59 0.86 0.66 1.12 243 112 0.85 0.70 1.02
3.ER+/PR+
NH White 3,195 1,077 1.00 Reference 13,176 5,561 1.00 Reference
Black 728 323 1.60 1.41 1.82 1,847 870 1.25 1.16 1.34
Hispanic White 787 234 1.00 0.87 1.15 1,288 483 0.97 0.89 1.07
API 444 131 0.98 0.82 1.17 909 301 0.85 0.76 0.95
4. ER−/PR−
NH White 2,187 1,142 1.00 Reference 6,304 3,615 1.00 Reference
Black 983 565 1.22 1.10 1.35 1,731 1,026 1.15 1.07 1.24
Hispanic White 592 278 0.96 0.84 1.09 798 410 0.98 0.88 1.08
API 280 134 1.03 0.86 1.24 603 279 0.79 0.70 0.89
5. Non-IBC and ER+/PR+
NH White 2,647 870 1.00 Reference 11,623 4,937 1.00 Reference
Black 601 257 1.60 1.39 1.85 1,633 766 1.25 1.16 1.35
Hispanic White 635 178 1.03 0.87 1.21 1,118 417 0.96 0.87 1.07
API 388 109 0.94 0.77 1.15 825 263 0.82 0.72 0.93
6. IBC and ER+/PR+
NH White 548 207 1.00 Reference 1,553 624 1.00 Reference
Black 127 66 1.80 1.35 2.40 214 104 1.28 1.03 1.59
Hispanic White 152 56 0.96 0.71 1.30 170 66 1.13 0.87 1.46
API 56 22 1.30 0.83 2.04 84 38 1.22 0.88 1.70
7. Non-IBC and ER−/PR−
NH White 1,497 748 1.00 Reference 4,710 2,697 1.00 Reference
Black 722 396 1.21 1.07 1.37 1,383 801 1.12 1.04 1.22
Hispanic White 408 180 0.97 0.82 1.14 593 301 0.98 0.87 1.11
API 217 102 1.09 0.89 1.35 485 218 0.80 0.70 0.92
8. IBC and ER−/PR−
NH White 690 394 1.00 Reference 1,594 918 1.00 Reference
Black 261 169 1.26 1.05 1.53 348 225 1.32 1.14 1.53
Hispanic White 184 98 0.93 0.74 1.16 205 109 0.98 0.80 1.20
API 63 32 0.88 0.61 1.27 118 61 0.80 0.61 1.04
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a

HR Hazard ratio, adjusted for: age at diagnosis, marital status, stage, grade, surgery, radiation, ER/PR status, and IBC status. The stratified variables were not included in stratified models.

IBC=Inflammatory breast cancer, NH=Non-Hispanic, API=Asian/Pacific Islander

Discussion

Black women had significantly worse survival compared to NHW women regardless of inflammatory status, hormone receptor status, and age group in our study of stage III and IV breast cancer. Conversely, API women tended to have the better breast cancer survival compared to NHW women, despite inflammatory histology or ER/PR status. The better survival among API women was observed for most groups defined by a combination of inflammatory and ER/PR states. HW and NHW women tended to have similar survival regardless of inflammatory and ER/PR states. In general, we found that racial/ethnic differences in breast cancer survival might be similar despite inflammatory histology and hormone receptor status.

Racial/ethnic differences in survival may relate to various factors such as accessibility to medical care, use of medical care, and tumor pathologic and biological features. Our study found similar racial/ethnic differences regardless of tumor characteristics (hormone receptor status and inflammatory histology). This is consistent with some previous studies, which also suggested similar racial/ethnic difference for breast cancer with various pathologic features (23, 24). These research results imply that factors other than these tumor features may play a large role in racial/ethnic disparities in breast cancer survival.

Use of medical care may be a major factor explaining the identified racial/ethnic disparities. It has been documented that, on average, blacks have a lower level of access to health care compared to whites (25). Therefore, they are less likely to have timely diagnosis and treatment, receive standard treatment, and complete follow-up surveillance and care than white patients (26–29). It is also well demonstrated that black patients were more likely to present with clinically-detected cancers rather than screen-detected cancer, and have delayed diagnoses compared to white patients (26). Many, but not all (30–32), studies found that black patients are more likely to have delayed treatment (26, 29, 33, 34) and are less likely to receive definitive primary therapy and adjuvant chemotherapy (34–38), hormonal therapy (30), radiation after lumpectomy (29, 39, 40) or mastectomy (41) than their white counterparts. While research on racial disparity in follow-up care has been sparse, it has been suggested that black patients may receive less medical monitoring or follow-up care (28). As a result of the racial disparities in diagnosis, treatment, and follow-up care, black patients may have worse survival than whites across different breast cancer types including inflammatory histology and ER/PR status. Our study also showed that the racial difference in survival appeared larger for patients younger than 50 years than those older among the patients with ER+/PR+. A similar result was observed previously in a study that suggested that Medicare availability for older women might help reduce racial differences in cancer care (42).

We do not exclude the possibility that biological features other than inflammatory histology and hormone receptor status may be related to the racial/ethnic differences in survival. For example, black patients may be more likely to have tumors with negative status of human epidermal growth factor-like receptor 2 (HER2) (43, 44) or P53 mutation (45), which are related to survival (43, 46–48). Although inconsistent (43, 47, 48), some studies on triple negative breast cancer, which included HER2- in addition to ER+/PR+, have found no racial differences in survival (49–51), suggesting a minimal potential impact of HER2 on racial differences . Therefore, there is a possibility that biomarkers of breast cancer other than inflammatory histology and ER/PR status may be associated with racial/ethnic disparities in survival in addition to the access to and use of medical care. Our finding of better survival among API women than whites is consistent with previous studies (52, 53). Similar to our study, an earlier SEER-based study found that, after adjusting for potential confounding variables, Asians experience significantly better survival compared to NHWs regardless of ER/PR status (13). It is largely unclear what factors may account for the survival differences between APIs and other racial/ethnic groups because data on Asians have been limited and research results have been inconsistent. Some studies have shown that Asian women were more likely to adhere to adjuvant hormonal therapy (54) or have follow-up mammography (55) than white women. However, other studies found no differences between Asian and white women in the receipt of adjuvant radiation treatment after breast conserving surgery (BCS) (56) but Asian women were less likely to undergo BCS than whites (57). Therefore, research is warranted on the role of medical care and other factors on survival differences between Asians and other racial/ethnic groups.

While the large dataset from the SEER registries makes it possible to assess racial/ethnic differences in survival by both inflammatory histology and ER/PR status, the limitations of this study should be kept in mind. The study was based on the existing data from the cancer registries; therefore, the effects of confounding factors that are not contained in the dataset cannot be excluded. For example, information on cancer treatment is not complete and detailed in the SEER data, precluding us from having solid assessment of and control for its potential effects on the results. Lack of individual-level information on socioeconomic status, which is related to breast cancer survival and correlated with racial/ethnic background (58), prevented us from controlling for its impacts in the analyses. This analysis was limited to cancer stages III and IV based on the definition of IBC. Thus, the results on ER/PR reflect only those for these tumor stages rather than all stages including stages I and II.

In conclusion, our study found that racial/ethnic disparities in breast cancer survival persist despite inflammatory histology and hormone receptor status. These results imply that factors other than inflammatory histology and hormone receptor status, such as access to or use of medical care, and/or other biomarkers, may play a role in racial/ethnic disparities in breast cancer survival.

Acknowledgments

This project was supported by John P. Murtha Cancer Center, Walter Reed National Military Medical Center via the Uniformed Services University of the Health Sciences under the auspices of the Henry M. Jackson Foundation for the Advancement of Military Medicine.

The authors thank Dr. Lindsey Enewold at the National Cancer Institute for her comments on the manuscript. This project was supported by John P. Murtha Cancer Center, Walter Reed National Military Medical Center via the Uniformed Services University of the Health Sciences under the auspices of the Henry M. Jackson Foundation for the Advancement of Military Medicine.

Abbreviations

IBC

Inflammatory breast cancer

ER

Estrogen receptor

PR

progesterone receptor

NHW

non-Hispanic white

HW

Hispanic white

API

Asian/Pacific Islander

SEER

Surveillance Epidemiology, and End Results

HR

hazard ratios

CI

confidence intervals

Footnotes

Conflicts of interest: The authors declare that they have no conflict of interest.

Publisher's Disclaimer: Disclaimer

The opinions and assertions expressed in this article represent the private views of the authors and do not reflect the official views of the U.S. Departments of the Army, Navy, or Defense, National Cancer Institute, or U.S. Government. Nothing in the presentation implies any Federal/Department of Defense/Department of the Navy endorsement.

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