Mammary analog secretory carcinoma (MASC) is a rare salivary gland tumor that was initially described in 2010.1 These tumors are characterized by a chromosomal translocation that fuses the ETS variant 6 gene (ETV6) (OMIM 600618) to the neurotrophic tyrosine kinase receptor type 3 (NTRK3) gene (OMIM 191361) and have histologic features similar to those of breast secretory carcinoma, a low-grade ductal breast carcinoma. Thus far, fewer than 300 cases have been reported in the literature. Studies have primarily been case reports and case series that focused on histopathologic and epidemiologic data. We aimed to use a population-based study of MASC cases to elucidate characteristic clinical features of this malignant tumor.
We used the Surveillance, Epidemiology, and End Results (SEER) database (SEER-18 registry, November 2017) to identify cases of MASC diagnosed from January 1, 2010, to December 31, 2015. Patients with MASC were identified using the International Classification of Diseases for Oncology, Third Edition (ICD-O-3) code 8502 and primary site of salivary gland. Data collected included sex, race, age, primary site, primary surgery, lymph node surgery, lymph node involvement, stage, cause-specific survival, grade, and duration of follow-up. De-identified data were obtained using SEER*Stat, version 8.3.5 (http://www.seerstat.gov); therefore, institutional review board approval was not required according to the University of California, Irvine, Office of Research.
Fifty-five patients with MASC (mean [SD] age, 48.6 [17.9] years; age range, 12-82 years; 31 [56.4%] male; 45 [81.8%] white) were identified in the SEER database. Patient demographic information, tumor characteristics, and treatment are summarized in the Table. Mean (SD) follow-up was 20.3 (14.9) months. Most patients had disease staged as American Joint Committee on Cancer stage I (25 [45.5%]) or II (18 [32.7%]) at diagnosis. Tumors were primarily located within the parotid gland (42 [76.4%]), and the most common primary operation performed was subtotal parotidectomy or subtotal removal of major salivary gland (25 [45.5%]). Thirty-four patients (61.8%) received a neck dissection for nodal management; however, nodal disease was found in only 3 patients (5.5%). No patients had distant metastatic disease. In patients for whom data were available, tumors were histologic grade I or II. All patients were alive at the conclusion of the study period, and length of survival correlated with year of diagnosis.
Because of the rarity of MASC, little information is available regarding the clinical characteristics of this neoplasm. To our knowledge, this study represents the largest described novel cohort of patients with MASC. Our results suggest that most patients have early-stage disease at presentation with rare nodal involvement. This finding is consistent with prior studies2,3 that have described MASC as a predominantly low-grade malignant tumor with an indolent clinical course. Although there have been case reports of MASC with high-grade transformation,4 no evidence of such aggressive cases was identified in this analysis.
Although 34 patients with MASC (61.8%) underwent neck dissection, only 3 patients (5.5%) had nodal metastasis. Other case series have demonstrated higher rates of nodal metastasis, with frequencies ranging from 6.7% to 25%.1,2,5 In this cohort, 61.8% of patients received neck dissections for nodal management, similar to the proportion reported by Chiosea et al (50%).5 However, Sethi et al6 described a lower rate of 22.8% in a combined analysis of 92 patients. Because many of the case series have a limited number of patients, further analysis is warranted to determine whether the frequency of neck dissections for clinical N0 disease is appropriate for the rate of nodal metastasis.
The duration of follow-up was limited because of the recent period in which this malignant tumor has been described. As a result, data were insufficient to determine prognostic factors that affect survival or disease management. Despite the limitations and small sample size of this study, our results suggest that MASC is a rare, indolent malignant tumor with a low rate of nodal metastasis.
Accepted for Publication: August 28, 2018.
Corresponding Author: Tjoson Tjoa, MD, Department of Otolaryngology–Head and Neck Surgery, University of California, Irvine, 101 The City Dr S, Bldg 56, Ste 500, Orange, CA 92868 (tjoat@uci.edu).
Published Online: November 8, 2018. doi:10.1001/jamaoto.2018.2936
Author Contributions: Dr Anderson had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: Haidar, Tjoa.
Study concept and design: Anderson.
Acquisition, analysis, or interpretation of data: Anderson, Armstrong, Tjoa.
Drafting of the manuscript: Anderson, Tjoa.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Anderson, Tjoa.
Supervision: Haidar, Tjoa.
Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.
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