Adjuvant Radiotherapy in pT1‐2N0M0 Head and Neck Adenoid Cystic Carcinoma

ABSTRACT

Background

Evidence regarding the indications and survival benefit of adjuvant radiotherapy (aRT) in pT1‐2N0M0 head and neck adenoid cystic carcinoma (HNAdCC) is inconclusive. Lower‐staged, node‐negative HNAdCC therefore represents a rare, moderate‐risk disease category with high variation in adjuvant management depending on patient and physician preferences. Our study investigates the impact of aRT on overall survival (OS) in this rare, moderate‐risk disease category.

Methods

The 2006 to 2018 National Cancer Database was retrospectively reviewed for patients with pT1‐2N0M0 HNAdCC. Multivariable binary logistic and Cox regression models were implemented.

Results

Of 738 patients satisfying inclusion criteria, 379 (51.4%) underwent aRT. Oral cavity primary site (aOR 0.64, 95% CI 0.43–0.96) was associated with lower odds of undergoing aRT (p < 0.05); neck dissection (aOR 1.58, 95% CI 1.09–2.28) and PSM (aOR 1.84, 95% CI 1.30–2.60) were associated with higher odds of undergoing aRT (p < 0.025). Patients undergoing aRT had higher 5‐year (94% vs. 86%) and 10‐year OS (85% vs. 73%) than those not undergoing aRT (p < 0.001). Adjusting for patient demographics, pathologic features, and treatment, age at diagnosis (aHR 1.05, 95% CI 1.02–1.08, p < 0.001) was associated with worse OS; aRT (aHR 0.30, 95% CI 0.13–0.69, p = 0.005) was associated with higher OS.

Conclusion

Approximately half of patients with pT1‐2N0M0 HNAdCC did not undergo aRT, highlighting a possible deviation from evidence‐based recommendations and an opportunity for quality improvement in the multidisciplinary care of patients. aRT was associated with higher 5‐year and 10‐year OS, suggesting that patients with lower‐staged, node‐negative HNAdCC should be offered aRT to optimize long‐term survival.

Level of Evidence

4.

pT1‐2N0M0 adenoid cystic carcinoma of the head and neck represents a rare, moderate‐risk disease category with high variation in treatment strategies, due to the inconsistent data on the survival benefit of adjuvant radiotherapy in lower‐staged disease. Our study of this disease category suggests that adjuvant radiotherapy is associated with higher 5‐year overall survival.

1. Introduction

Adenoid cystic carcinoma (AdCC) accounts for < 1% of head and neck cancer (HNC) and occurs most frequently in the major salivary glands, sinonasal tract, and larynx [1, 2, 3, 4, 5, 6, 7, 8]. Head and neck adenoid cystic carcinoma (HNAdCC) has an indolent course but exhibits a predilection for perineural invasion (PNI), locoregional recurrence, and distant metastasis, even many years after initial diagnosis and treatment [9, 10, 11]. Regional lymph node metastasis is relatively rare, but hematogenous metastasis to the lung, bone, and liver is common [12, 13].

Surgery achieving negative margins is the preferred primary, curative treatment of non‐metastatic HNAdCC. Evidence‐based recommendations made by the National Comprehensive Cancer Network (NCCN) consider AdCC histology as an indication for adjuvant radiotherapy (aRT), especially in the presence of other adverse features such as extranodal extension (ENE), lymphovascular invasion (LVI), positive or close surgical margins, and PNI [14, 15, 16, 17, 18, 19, 20]. Although aRT is pursued for the majority of patients with HNAdCC, evidence regarding the indications and survival benefit of aRT in pT1‐2N0M0 HNAdCC is inconclusive [11, 21, 22, 23, 24, 25]. HNAdCC also has reportedly decreased radiosensitivity and aRT is associated with treatment‐induced toxicities such as xerostomia, stiffness, paresthesia, dysgeusia, hoarseness, and lymphedema. Lower‐staged, node‐negative HNAdCC therefore represents a rare, moderate risk disease category with high variation in adjuvant management depending on patient and physician preferences [26, 27, 28]. In addition, the rate of aRT utilization in these patients has yet to be characterized with a large, nationally representative cohort. Our study of the National Cancer Database (NCDB) investigates aRT utilization and associated differences in overall survival (OS) in pT1‐2N0M0 HNAdCC. To our knowledge, our study is also the first to present a cohort exclusively of patients with pT1‐2N0M0 HNAdCC.

2. Methods

2.1. Data Source

The NCDB, a national, hospital facility‐based, comprehensive clinical surveillance resource established in 1989, is jointly sponsored by the American Cancer Society and American College of Surgeons (ACS) Commission on Cancer (CoC), contains data derived from > 1500 CoC‐accredited hospitals, and captures > 70% of all newly diagnosed cancers in the United States annually [29, 30]. The ACS has executed a Business Associate Agreement that includes a data use agreement with each of its CoC‐accredited hospitals. This study was deemed exempt from review by the Rutgers New Jersey Medical School Institutional Review Board because of the de‐identified nature of patient data. The ACS and CoC have not verified and are not responsible for the validity of the statistical analysis or conclusions derived herein.

2.2. Inclusion Criteria

The 2006 to 2018 NCDB was retrospectively reviewed for adults with pT1‐2N0M0 HNAdCC undergoing surgery with curative intent (Figure 1). HNAdCC was identified using International Classification of Diseases for Oncology, Third Edition (ICD‐O‐3) histology (“8200”), behavior (“3”), and topography (“C00,” “C02.0,” “C02.1,” “C02.2,” “C02.3,” “C02.8,” “C02.9,” “C03,” “C04,” “C05.0,” “C05.8,” “C05.9,” and “C06” for oral cavity; “C07” and “C08” for major salivary glands; “C11,” “C30.0,” and “C31” for sinonasal tract; “C01,” “C02.4,” “C05.1,” “C05.2,” “C09,” and “C10” for oropharynx; “C12” and “C13” for hypopharynx; and “C32” for larynx) codes. Patients were excluded if they had a history of prior malignancy; carcinoma in situ (i.e., pTis); pathologic nodal disease; treatment with palliative intent; aRT initiated > 90 days after surgery (i.e., salvage radiotherapy) or completed > 8 weeks after initiation; treatment with chemotherapy regardless of type and number of agents; neoadjuvant radiotherapy or systemic therapy; unknown pathologic tumor‐nodal‐metastasis (pTNM) classification, aRT status, chemotherapy status, vital status, or survival time; unknown aRT timing, dose, modality, volume, or duration; or unknown sequence of surgery, radiotherapy, and systemic therapy [31].

FIGURE 1.

Inclusion criteria. Patients satisfying ≥ 1 criterion are counted for each individual criterion, resulting in slight discrepancies in sample size (i.e., “double counting”). aRT, adjuvant radiotherapy; LVI, lymphovascular invasion; NCDB, National Cancer Database; pTN, pathologic tumor‐nodal.

2.3. Variables

Patient data included age at diagnosis, sex, race, Charlson‐Deyo comorbidity score (CDCS), history of prior malignancy, histology, primary site, grade, pTNM classification, LVI, neck dissection, surgical margins, surgical length of stay (LOS), 30‐day unplanned readmission and 90‐day mortality following surgery, adjuvant therapy, vital status, and survival time. A CDCS of 0 indicates no comorbid medical conditions [32]. Surgery was defined based on previous studies of the NCDB and included local tumor destruction, local tumor excision, partial removal, total removal, radical removal, and unspecified resection [33]. Neck dissection was defined as the removal and examination of $\ge$ 10 lymph nodes, a threshold validated by previous studies of HNC [34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44]. PSM included microscopic, macroscopic, or unspecified residual tumor. aRT was defined as the delivery of therapeutic doses (40–80 Gy) of external beam radiation to the head and neck, initiated $\le$ 90 days after surgery and completed $\le$ 8 weeks after initiation, aligning with parameters set by previous studies for aRT in HNC [31, 33, 45]. The primary outcome of our study was 5‐year OS. Survival time was calculated as the time from diagnosis to either death or 5 years of follow‐up.

2.4. Statistical Analysis

Patients were divided into two cohorts based on aRT status. The distributions of categorical variables were compared using the chi‐square test. The Shapiro–Wilk test was used to assess the normality of continuous variables; median, interquartile range (IQR), and Mann–Whitney U significance were reported. A multivariable binary logistic regression model adjusting for all variables significant in univariable regression was implemented to identify patient demographics and pathologic features independently associated with undergoing aRT. Kaplan–Meier analysis with the log‐rank test was implemented to estimate 5‐year OS. Multivariable Cox proportional hazards regression analyses included patient demographics, pathologic features, and treatment significant in univariable Cox regression. The proportionality of hazards assumption was evaluated using time‐dependent covariables and was not violated in any regression models. Multivariable regression models utilized listwise elimination (i.e., complete‐case analysis) for missing data, resulting in the exclusion of patients missing data for ≥ 1 covariables and slight discrepancies in sample size, as documented in the table footnotes. Statistical significance was indicated with a two‐sided alpha level of 0.05 (i.e., p < 0.05). SPSS version 25 (IBM) and Microsoft Excel (Microsoft) were used for statistical analysis.

3. Results

3.1. Patient Demographics, Pathologic Features, and Treatment

A total of 738 patients satisfied inclusion criteria. Median (IQR) patient age was 57 (46–68) years. Most patients were female (N = 449, 60.8%), of White race (N = 576, 79.3%), and had a CDCS of 0 (N = 617, 83.6%). A high proportion of patients had disease of the major salivary glands (N = 505, 68.4%) classified as moderately differentiated (N = 173, 45.4%) and pT1 (N = 397, 53.8%) without LVI (N = 421, 91.5%) and with negative surgical margins (N = 519, 72.2%). 560 (76.8%) patients underwent neck dissection. Following surgery, median (IQR) LOS was 1 (0–2) days, 13 (1.9%) patients had unplanned 30‐day readmission, and 3 (0.4%) patients had 90‐day mortality.

About 359 (48.6%) patients did not undergo aRT and 379 (51.4%) underwent aRT. aRT utilization was highest in 2015 (64%) and decreased to 43% in 2018 (R ² = 0.0168) (Figure 2). Median (IQR) time from surgery to aRT initiation was 43 (36–54) days. Median (IQR) aRT dose was 60 (60–66) Gy and median (IQR) aRT duration was 45 (43–48) days. Patients undergoing aRT more frequently were younger (median [IQR] 55 [45–66] vs. 59 [48–79] years), had pT2 disease (50.1% vs. 42.1%), underwent neck dissection (26.9% vs. 19.3%), and had PSM (34.1% vs. 21.2%) (p < 0.05) (Table 1). aRT utilization was highest in patients aged 40–49 years (58%) and lowest in patients aged $\ge$ 80 years (23%) (R ² = 0.480) (Figure 3).

FIGURE 2.

Proportion of patients undergoing aRT over the study period (2006–2018). aRT, adjuvant radiotherapy. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]

TABLE 1.

Patient demographics, pathologic features, and treatment, n (%).

	No aRT	aRT	p	Total
No.	359	379	—	738
Age at diagnosis, median years (IQR)	59 (48–70)	55 (45–66)	0.002	57 (46–68)
Sex
Male	149 (41.5)	140 (36.9)	0.204	289 (39.2)
Female	210 (58.5)	239 (63.1)		449 (60.8)
Race
White	283 (79.9)	293 (78.8)	0.920	576 (79.3)
Black	38 (10.7)	43 (11.6)		81 (11.2)
Other	33 (9.3)	36 (9.7)		69 (9.5)
Charlson‐Deyo comorbidity score
0	301 (83.8)	316 (83.4)	0.530	617 (83.6)
1	44 (12.3)	42 (11.1)		86 (11.7)
$\ge$ 2	14 (3.9)	21 (5.5)		35 (4.7)
Primary site
Oral cavity	81 (22.6)	54 (14.2)	0.026	135 (18.3)
Major salivary glands	228 (63.5)	277 (73.1)		505 (68.4)
Sinonasal tract	22 (6.1)	17 (4.5)		39 (5.3)
Oropharynx	24 (6.7)	24 (6.3)		48 (6.5)
Hypopharynx, larynx	4 (1.1)	7 (1.8)		11 (1.5)
Grade
Well differentiated	83 (45.9)	78 (39.0)	0.251	161 (42.3)
Moderately differentiated	80 (44.2)	93 (46.5)		173 (45.4)
Poorly differentiated, undifferentiated, anaplastic	18 (9.9)	29 (14.5)		47 (12.3)
pT classification
1	208 (57.9)	189 (49.9)	0.028	397 (53.8)
2	151 (42.1)	190 (50.1)		341 (46.2)
Lymphovascular invasion
No	206 (92.4)	215 (90.7)	0.523	421 (91.5)
Yes	17 (7.6)	22 (9.3)		39 (8.5)
Neck dissection
No	285 (80.7)	275 (73.1)	0.015	560 (76.8)
Yes	68 (19.3)	101 (26.9)		169 (23.2)
Surgical margins
Negative	275 (78.8)	244 (65.9)	< 0.001	519 (72.2)
Positive	74 (21.2)	126 (34.1)		200 (27.8)

Note: Bolded values indicate statistical significance (p < 0.05).

Abbreviations: aRT, adjuvant radiotherapy; IQR, interquartile range; pT, pathologic tumor.

FIGURE 3.

Proportion of patients undergoing aRT by age at diagnosis. aRT, Adjuvant radiotherapy. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]

On multivariable binary logistic regression adjusting for patient demographics and pathologic features (i.e., pT classification and surgical margins), age at diagnosis (adjusted odds ratio [aOR] 0.99, 95% confidence interval [CI] 0.98–0.99) and oral cavity primary site (aOR 0.64, 95% CI 0.43–0.96) were associated with lower odds of undergoing aRT (p < 0.05); neck dissection (aOR 1.58, 95% CI 1.09–2.28) and PSM (aOR 1.84, 95% CI 1.30–2.60) were associated with higher odds of undergoing aRT (p < 0.025) (Table 2).

TABLE 2.

Univariable and multivariable binary logistic regression models for undergoing aRT.

	Univariable		Multivariable
	OR (95% CI)	p	aOR a (95% CI)	p
Age at diagnosis, years	0.98 (0.98–0.99)	< 0.001	0.99 (0.98–0.99)	0.003
Sex
Male	Ref
Female	1.21 (0.90–1.63)	0.204
Race
White	Ref
Black	1.09 (0.69–1.74)	0.708
Other	1.05 (0.64–1.74)	0.838
Charlson‐Deyo comorbidity score
0	Ref
1	0.91 (0.58–1.43)	0.679
$\ge$ 2	1.43 (0.71–2.86)	0.314
Primary site
Oral cavity	0.55 (0.37–0.81)	0.002	0.64 (0.43–0.96)	0.030
Major salivary glands	Ref		Ref
Sinonasal tract	0.64 (0.33–1.23)	0.177	0.78 (0.39–1.57)	0.482
Oropharynx	0.82 (0.46–1.49)	0.519	0.84 (0.46–1.54)	0.574
Hypopharynx, larynx	1.44 (0.42–4.98)	0.564	1.28 (0.35–4.71)	0.709
Grade
Well differentiated	Ref
Moderately differentiated	1.24 (0.81–1.90)	0.332
Poorly differentiated, undifferentiated, anaplastic	1.71 (0.88–3.33)	0.112
pT classification
1	Ref		Ref
2	1.39 (1.04–1.85)	0.028	1.19 (0.87–1.62)	0.277
Lymphovascular invasion
No	Ref
Yes	1.24 (0.64–2.40)	0.572
Neck dissection
No	Ref		Ref
Yes	1.54 (1.09–2.18)	0.015	1.58 (1.09–2.28)	0.015
Surgical margins
Negative	Ref		Ref
Positive	1.92 (1.37–2.68)	< 0.001	1.84 (1.30–2.60)	< 0.001

Note: Bolded values indicate statistical significance (p < 0.05).

Abbreviations: aOR, adjusted odds ratio; aRT, adjuvant radiotherapy; OR, odds ratio; pT, pathologic tumor; Ref, reference.

^a N = 710; number of events: 367.

Among 359 patients not undergoing aRT, the most cited reasons were not part of the planned treatment course (N = 291, 81.1%) and recommended by physician but refused by patient or family (N = 46, 12.8%).

3.2. Five‐Year OS

Patients undergoing aRT had higher 5‐year OS than those not undergoing aRT (94% vs. 86%, p < 0.001; Figure 4) (Table 3). aRT was associated with higher 5‐year OS across a range of primary sites (oral cavity, major salivary glands, and oropharynx), pathologic features (i.e., grade, pT classification, LVI, and surgical margins), and treatment (i.e., neck dissection).

FIGURE 4.

Kaplan–Meier analysis of 5‐year OS among 359 patients not undergoing aRT and 379 patients undergoing aRT (p < 0.001). Significance is derived from the log‐rank test. aRT, adjuvant radiotherapy; OS, overall survival. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]

TABLE 3.

Kaplan–Meier analysis of 5‐year OS.

	No aRT	aRT	p
Overall	86	94	< 0.001
Primary site
Oral cavity	82	96	0.006
Major salivary glands	88	94	0.049
Sinonasal tract	82	93	0.555
Oropharynx	86	95	0.025
Hypopharynx, larynx	71	85	0.950
Grade
Well differentiated	91	94	0.540
Moderately differentiated	83	96	0.007
Poorly differentiated, undifferentiated, anaplastic	61	83	0.011
pT classification
1	88	98	0.002
2	84	90	0.007
Lymphovascular invasion
No	89	97	0.002
Yes	79	94	0.079
Neck dissection
No	84	94	0.002
Yes	93	93	0.034
Surgical margins
Negative	89	97	0.003
Positive	77	90	0.002

Note: Bolded values indicate statistical significance (p < 0.05).

Abbreviations: aRT, adjuvant radiotherapy; OS, overall survival; pT, pathologic tumor.

On multivariable Cox regression adjusting for patient demographics, pathologic features (i.e., grade, pT classification, LVI, and surgical margins), and treatment, age at diagnosis (adjusted hazard ratio [aHR] 1.05, 95% CI 1.02–1.08, p < 0.001) was associated with worse OS; aRT (aHR 0.30, 95% CI 0.13–0.69, p = 0.005) was associated with higher OS (Table 4). Sex, race, CDCS, primary site, grade, pT classification, neck dissection, and surgical margins were not significantly associated with OS.

TABLE 4.

Univariable and multivariable Cox proportional hazard regression models.

	Univariable		Multivariable
	HR (95% CI)	p	aHR a (95% CI)	p
Age at diagnosis, years	1.05 (1.04–1.07)	< 0.001	1.05 (1.02–1.08)	< 0.001
Sex
Male	Ref
Female	0.78 (0.54–1.14)	0.782
Race
White	Ref
Black	1.51 (0.90–2.54)	0.121
Other	0.56 (0.23–1.37)	0.204
Charlson‐Deyo comorbidity score
0	Ref
1	0.99 (0.57–1.75)	0.995
$\ge$ 2	1.04 (0.45–2.37)	0.932
Primary site
Oral cavity	1.35 (0.85–2.15)	0.208
Major salivary glands	Ref
Sinonasal tract	1.45 (0.67–2.16)	0.350
Oropharynx	1.18 (0.57–2.45)	0.661
Hypopharynx, larynx	2.00 (0.63–6.34)	0.241
Grade
Well differentiated	Ref		Ref
Moderately differentiated	1.21 (0.66–2.24)	0.536	1.46 (0.65–3.27)	0.364
Poorly differentiated, undifferentiated, anaplastic	2.89 (1.44–5.82)	0.003	1.68 (0.61–4.63)	0.318
pT classification
1	Ref		Ref
2	1.70 (1.16–2.48)	0.007	1.32 (0.62–2.82)	0.473
Lymphovascular invasion
No	Ref		Ref
Yes	2.60 (1.18–5.53)	0.017	1.37 (0.50–3.76)	0.547
Neck dissection
No	Ref
Yes	0.87 (0.55–1.39)	0.557
Surgical margins
Negative	Ref
Positive	1.50 (1.01–2.22)	0.045	1.30 (0.61–2.77)	0.504
aRT
No	Ref		Ref
Yes	0.50 (0.34–0.73)	< 0.001	0.30 (0.13–0.69)	0.005

Note: Bolded values indicate statistical significance (p < 0.05).

Abbreviations: aHR, adjusted hazard ratio; aRT, adjuvant radiotherapy; HR, hazard ratio; pT, pathologic tumor; Ref, reference.

^a N = 280; number of uncensored deaths: 31.

3.3. Ten‐Year OS

Patients undergoing aRT had higher 10‐year OS than those not undergoing aRT (85% vs. 73%, p < 0.001).

On multivariable Cox regression adjusting for patient demographics, pathologic features (i.e., grade, pT classification, LVI, and surgical margins), and treatment, undergoing aRT (aHR 0.31, 95% CI 0.14–0.72, p = 0.006) remained associated with higher OS.

4. Discussion

Surgery achieving negative margins is the preferred primary, curative treatment of non‐metastatic HNAdCC, and timely aRT has a documented survival benefit in the presence of high‐risk pathologic features such as LVI, ENE, PSM, and PNI. Evidence regarding the indications and survival benefit of aRT in lower‐staged, node‐negative HNAdCC is inconclusive; pT1‐2N0M0 HNAdCC therefore represents a rare, moderate‐risk disease category with high variation in adjuvant management depending on patient and physician preferences [26, 27, 28]. Our analysis of pT1‐2N0M0 HNAdCC using the NCDB suggests that aRT is utilized in approximately 50% of patients and is associated with higher OS.

A slight majority of patients (52%) in our cohort underwent aRT, contrasting with the NCCN recommendation that all patients with HNAdCC undergo aRT and underscoring the variability in patient and physician preferences regarding aRT in lower‐staged, node‐negative HNAdCC [18, 46]. In addition, aRT utilization appears to have peaked in 2015 and declined in recent years, representing a possible area for quality improvement in the multidisciplinary care of patients with HNAdCC.

Patients with higher odds of undergoing aRT were younger, had PSM, and underwent neck dissection. Younger patients likely benefit more from aRT because HNAdCC has a predilection for locoregional recurrence, even many years after initial diagnosis and treatment, with one study noting 5‐, 10‐, and 20‐year OS of 68%, 52%, and 28%, respectively [47, 48, 49, 50]. Our study supports the long‐term survival benefit associated with aRT (94% vs. 86% for 5‐year OS and 85% vs. 73% for 10‐year OS) suggesting that potential treatment‐induced toxicities (e.g., xerostomia, mucositis, dermatitis, dysphagia, feeding tube dependence, fibrosis, osteoradionecrosis, and carotid artery stenosis) are justified to optimize survival. Older patients tend to decline or are not offered aRT when the perceived benefits are marginal, representing a possible selection bias because these patients typically have shorter life expectancy, more comorbidities, and worse baseline performance status [51]. Nevertheless, our study suggests that aRT is associated with higher OS independent of patient age, highlighting the survival benefit of aRT in appropriately selected patients. Unsurprisingly, aRT was more commonly utilized in patients with PSM [52]. Lastly, patients undergoing neck dissection likely had a preoperative or intraoperative indication such as suspicious lymphadenopathy or close surgical margins and were offered aRT to promote complete tumor eradication even in the absence of pathologic nodal disease.

Our study associated aRT with higher 5‐ and 10‐year OS in patients with pT1‐2N0M0 HNAdCC, supporting NCCN recommendations favoring aRT in all patients with HNAdCC. A prior analysis of major salivary AdCC using the NCDB associated aRT with higher OS, even among patients with lower‐staged disease (i.e., pT1‐2N0) [53]. Our analysis of HNAdCC using the NCDB strengthens these findings, supporting the survival benefit of aRT across a range of primary sites and clinicopathologic features, including in patients without LVI and those with negative surgical margins. Importantly, our study did not evaluate novel aRT modalities such as intensity‐modulated radiotherapy and proton therapy, which offer improved precision in targeting the tumor bed and reduced treatment‐related toxicities while delivering higher radiation doses that spare healthy adjacent structures [54].

Approximately 25% of patients in our cohort underwent neck dissection, aligning with current evidence suggesting that neck dissections are not commonly performed because of the rarity of occult nodal metastasis in lower‐staged HNAdCC [55]. Neck dissection was not associated with higher OS. Advanced HNAdCC (i.e., pT‐3‐4) may mandate at least a limited neck dissection because of the higher frequency of occult nodal metastasis and more extensive resections requiring free flap reconstruction, but these patients were excluded in our cohort [56].

Our patient cohort largely consists of White females, who may represent a higher socioeconomic group [57]. Given the time commitment of undergoing aRT, including daily visits to the treatment facility over several weeks, aRT may be less feasible for patients with lower socioeconomic status; income, education, and distance to the treatment facility are examples of social determinants of health that contribute to disparities in provider access, treatment, and outcomes [58].

The strengths of our study are strict inclusion criteria, large sample size of a rare tumor presentation, and comprehensive reporting of 5‐year OS by aRT status. Although our study draws from a large, nationally representative network of hospital facilities, several limitations warrant acknowledgement. Retrospective review of the NCDB inherently introduces the possibility of inaccurate histologic diagnosis and variable miscoding, limiting analysis to measures of correlation rather than causation. The NCDB does not report medical comorbidities, tobacco use, prior radiotherapy, imaging, PNI, depth of invasion, extent of LVI, close margins, multidisciplinary tumor board recommendations, quality of life, locoregional recurrence, and disease‐free survival; these considerations are important because of the predilection of HNAdCC for recurrence and may have impacted the decision to pursue aRT [15]. The NCDB also does not adequately report why some patients with PSM, a well‐documented adverse pathologic feature, did not undergo aRT. Moreover, the simplification of aRT to a binary outcome limits consideration of treatment delays, interruptions, and extent of completion [38]. Defining neck dissection as the removal and examination of ≥ 10 lymph nodes may overestimate the delivery of neck dissection and include patients undergoing more selective nodal resections [37]. Despite these limitations, our study utilizing the NCDB associated aRT with higher OS in patients with pT1‐2N0M0 HNAdCC.

5. Conclusion

Approximately half the patients in our cohort with pT1‐2N0M0 HNAdCC did not undergo aRT, highlighting a significant deviation from NCCN recommendations and an opportunity for quality improvement in the multidisciplinary care of these patients. Patients undergoing aRT more frequently were younger, underwent neck dissection, and had PSM. Adjusting for patient demographics, pathologic features, and treatment, aRT was independently associated with higher 5‐ and 10‐year OS. Additional studies are warranted to further clarify adjuvant management of this rare, moderate‐risk category, and which patients can safely avoid aRT.

Conflicts of Interest

The authors declare no conflicts of interest.

Kaki P. C., Patel A. M., Haleem A., et al., “Adjuvant Radiotherapy in pT1‐2N0M0 Head and Neck Adenoid Cystic Carcinoma,” The Laryngoscope 135, no. 9 (2025): 3202–3212, 10.1002/lary.32156.