[Non-primary solid malignancies of breast in needle core biopsy: a clinicopathological analysis of 23 cases].

Objective: To investigate the accurate diagnosis and differential diagnosis of non-primary solid malignant tumors in breast needle core biopsy. Methods: Twenty-three cases of breast, axilla or neck lymph nodes pathologically diagnosed as non-primary solid malignant tumors were collected at the First Affiliated Hospital of Nanjing Medical University, Nanjing, China from January 2013 to March 2023. The differential diagnoses and diagnostic features were analyzed, based on combining clinical data, histology, and expression characteristics of biomarkers. Results: All patients were female, with age ranging from 29 to 75 years (average 56 years). The average time from the diagnosis of primary tumor to the current diagnosis was 21 months (0 to 204 months).The primary sites included the ovary (9 cases), the lung (5 cases), the gastrointestinal tract (4 cases), the pancreas, intrahepatic bile duct, thyroid gland, nasal cavity and forearm skin (1 case each). No carcinoma in situ was found in any of the cases. The morphological differences were significant among the tumors, but similar to the primary tumors. The tumors of neuroendocrine and female reproductive tract had great morphological and immunophenotypic overlaps with breast cancer. Metastatic lung cancer cells showed obvious atypia and tumor giant cells. The morphology and immunophenotype of metastatic serous carcinoma of female reproductive system might resemble invasive micropapillary carcinoma of the breast. Metastatic adenocarcinoma of the gastrointestinal tract often had features of mucous secretion. Metastatic neuroendocrine tumors were bland in appearance and morphologically similar to solid papillary carcinoma of breast, but negative for ER. TRPS1 was mostly negative (18/23) and variably positive in ovarian (4/9) and intrahepatic bile duct (1/1) tumors. Conclusions: The diagnosis of breast needle core biopsy specimen should be combined with clinical history, imaging study, and careful examination of histological features, such as presence of in situ component, morphological similarity between the primary and metastatic tumors, and using appropriate markers to differentiate the primary from metastatic tumors.