Abstract PO4-25-08: Secretory breast carcinoma (SBC) in an 8-year-old male: Report of an exceptionally rare case with review of clinicoradiologic and pathomolecular findings of SBC in the male pediatric population

Abstract Secretory breast carcinoma (SBC) is a rare and distinct disease, comprising approximately 0.01% of all breast carcinomas. This is a case of an 8-year-old boy who presented with a 1.5-year history of a non-tender, slowly enlarging left subareolar mass, not associated with nipple discharge. Serologic workup revealed minimally elevated prolactin with normal-range FSH, LH, estradiol and testosterone, as well as normal-range beta-hCG, LDH and AFP. Ultrasound showed a circumscribed solid hypoechoic lesion with internal arterial vascularity, favoured to represent a sebaceous cyst. Excisional biopsy was performed, and histologic examination revealed the classic intra- and extracellular secretory material typically seen in SBC. Immunohistochemical (IHC) stains for mammaglobin, S-100 and high molecular weight keratin (CK5) were positive. ER was positive, though not strong staining, and PR and HER2 were negative. A screen for NTRK fusions with pan-TRK IHC was positive. No skin, perineural or lymphovascular invasion was identified. RNA-based NGS demonstrated ETV6-NTRK3 fusion and confirmed the diagnosis of SBC. The patient underwent mastectomy and SLNB, which showed no residual tumor and no positive lymph nodes. A full metastatic work-up was not performed and the patient did not receive neoadjuvant therapy. First described as “juvenile breast carcinoma,” SBC has since been recognized to occur across a wide age range, with most cases occurring in adults. SBC in male pediatric patients is exceptionally rare, with fewer than 20 cases reported in the literature. In this demographic, SBC is usually detected clinically as a subareolar mass not associated with nipple discharge, and appears as a well-circumscribed mass on imaging, mimicking benign entities. SBC is usually detected at a low stage, treated surgically, and follows a clinically indolent course with excellent outcomes. Positive axillary nodes have been identified in a few male children, who subsequently underwent chemo- and/or radiotherapy, with no recorded recurrences in these cases. Distant metastases are an extremely uncommon feature of SBC and have not been reported in the pediatric male population; however, due to the rarity of this diagnosis, particularly in this demographic, robust long-term follow-up data are still lacking. The name “secretory” derives from the histologic appearance of the dense eosinophilic secretory material seen in tumor lumina and bubbly material in the cytoplasm of tumor cells. Similar to the cytologic characteristics of other translocation-driven neoplasms, SBC shows minimal pleomorphism. Mitoses are absent or rare. IHC stains are typically positive for S-100 and high molecular weight keratins and negative for ER, PR, and HER2. Despite the immunophenotypic similarities to triple negative/basal-like carcinomas (TNBC/BLC) the molecular relationship between SBC and TNBC/BLC is unclear. Though initially defined by its distinctive secretions on histology, SBC is now chiefly characterized by a balanced translocation, t(12;15)(p13;q25), resulting in oncogenic ETV6-NTRK3 fusion. Recent cases have demonstrated this using a variety of molecular techniques, including FISH, RT-PCR, and in our case, RNA-based NGS. This translocation also characterizes non-breast secretory carcinomas and has been identified in several other neoplasms, including pediatric mesenchymal tumours and adult acute myeloid leukemia. The rarity of SBC, particularly in the male pediatric population, underlines the necessity of this case report. Additionally, this case highlights the importance of considering SBC as a potential diagnosis in male children presenting with a breast mass, even in the presence of benign imaging characteristics. Table 1: Clinicoradiologic and pathomolecular characteristics of SBC in pediatric males AND, axillary node dissection; CT, chemotherapy; ER, estrogen receptor; FISH, fluorescence in situ hybridization; LE, local excision; MRM, modified radical mastectomy; nd, no data; NED, no evidence of disease; NGS, next-generation sequencing; NS, nodal sampling; PA, periareolar; PR, progesterone receptor; RA, retroareolar; RM, radical mastectomy; PCR, polymerase chain reaction; RT, radiotherapy; SA, subareolar; SLNB, sentinel lymph node biopsy; SM, simple mastectomy; WLE, wide local excision *Not reported as strong staining Table 2: Immunohistochemical phenotype of secretory breast carcinoma EMA, epithelial membrane antigen; ER, estrogen receptor; PR, progesterone receptor *Not reported as strong staining Table 3: Laboratory investigations AFP, alpha fetoprotein; FSH, follicle stimulating hormone; hCG, human chorionic gonadotropin; LDH, lactate dehydrogenase; LH, luteinizing hormone Citation Format: Rebecca Brassington, Svetlana Silverman, Ioana Bratu. Secretory breast carcinoma (SBC) in an 8-year-old male: Report of an exceptionally rare case with review of clinicoradiologic and pathomolecular findings of SBC in the male pediatric population [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-25-08.

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