Mammary analog secretory carcinoma (MASC)

• Mammary analog secretory carcinoma (MASC):
  • Is a recently described salivary gland tumor:
    • That was likely classified as acinic cell carcinoma in the past
• The tumor has striking histologic and molecular similarities:
  • To secretory carcinoma of the breast
• Secretory carcinoma of the breast (SC):
  • Has shown to have a recurrent balanced chromosomal translocation:
    • t(12;15) (p13;q25):
      • Which leads to an oncogenic fusion gene ETV6-NTRK3
  • This translocation is also present in MASC:
    • This fusion gene encodes a chimeric tyrosine kinase:
      • That is known to play an important role on its oncogenesis
• Immunohistochemical similarities between MASC and SC of the breast also include:
  • Being S100 protein, epithelial membrane antigen (EMA), and vimentin positive and “triple negative” (ER/PR/Her2 negative)
• MASC predominantly affects:
  • Men and normally does not behave in an aggressive biology
• The parotid gland is the most common affected gland by MASC

• The official terminology of this entity:
  • Is now “secretory carcinoma”
• At the histologic level:
  • Tumor cells have eosinophilic or clear bubbly cytoplasm:
    • They may grow as tubules or microcysts, papillae, or macrocysts
  • Secretions are almost always present:
    • In the microcysts and / or macrocysts
• MASC characteristically harbors:
  • A balanced chromosomal translocation (12, 15):
    • Resulting in the formation of the ETV6–NTRK3 fusion genes
• Even though they have similar growth rate between MASC and ACC:
  • MASC is more likely to metastasize to the regional lymph nodes:
    • It should be considered as a more aggressive tumor compared with the regular low grade ACC
• MASC usually presents as a painless:
  • It is a non-tender mass that increases in size overtime
• The majority of MASC arise from the parotid gland;
  • Accounting for two thirds of the reported cases
• The mean age for presentation of MASC is 47 years:
  • In contrast with SC of the breast that usually occurs in younger patients
• MASC:
  • Is considered a low-grade carcinoma with a favorable prognosis:
    • According to Skálová et al:
      • It has moderate risk for local recurrence (15%)
      • Lymph node metastases (20%)
      • Low risk for distant metastases (5%)

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