Secretory Carcinoma of the Breast Mimicking Invasive Ductal Carcinoma: A Case Report

BACKGROUND Secretory breast carcinoma (SBC), an extremely rare malignancy, is related to a chromosomal translocation which leads to an ETV6-NTRK3 fusion mutation. SBC is characterized by eosinophilic secretions and is usually triple-negative, with a small number of patients demonstrating ER-positivity of the tumors. Diagnosis can be challenging and requires genomic testing for confirmation. CASE REPORT A 40-year-old woman presented with a breast mass found on mammography. She underwent an ultrasound-guided biopsy of the tumor. Initial pathology evaluation revealed features consistent with invasive ductal carcinoma. The immunochemistry report described an ER-positive, PR-negative, and HER2-negative tumor. The specimen was sent for oncotype scoring, which was not performed due to the specimen not meeting the criteria for invasive ductal carcinoma and displaying pathological features of SBC. A fluorescent in situ hybridization (FISH) study revealed ETV6 translocation, consistent with the diagnosis of SBC. The patient underwent lumpectomy followed by adjuvant radiotherapy and endocrine therapy. She remains in complete remission 3 years after treatment. CONCLUSIONS Accurately diagnosing SBC is of extreme importance as it has an indolent clinical course, but has a favorable prognosis if detected early. Due to nonspecific imaging findings, pathology evaluation with immunohistochemical staining followed by genomic testing is required. Our case highlights the challenges associated with SBC diagnosis requiring genomic testing due to equivocal pathological findings, along with increasing incidence of SBT in adults. There are no established guidelines for SBC management. The mainstay of treatment is partial or total mastectomy. Data on the benefits of adjuvant endocrine therapy, chemotherapy, and radiotherapy are inconclusive.