Objective: To investigate the clinicopathological features, immunophenotype, diagnosis, and prognosis of invasive carcinoma originating from microglandular adenosis.

Methods: Two cases of invasive carcinoma originating from microadenosis were analyzed in the Department of Pathology of the Ruijin Hospital affiliated with the Medical College of Shanghai Jiaotong University. Histopathological morphology, immunohistochemical staining, and prognosis were observed.

Results: (1) Histopathological morphology: microscopically, the tumor showed small clusters and nests of infiltrative growth; a few areas showed tubules, and some eosinophilic secretions were observed in the lumen. (2) Immunohistochemistry and molecular genetics: Case 1 was partly positive for S-100, positive for SOX-10, and negative for ER, PR, and HER2 (2+). The result of HER2 gene amplification was negative. Breast and liver tissue lesions in Case 2 were positive for S-100 and SOX-10 but negative for ER and HER2. PR was positive in the liver lesions but showed moderate to strong expression in approximately 80% of the staining. Myoepithelial markers (p63 and calponin) showed loss of myoepithelium around the nests of invasive cancers. TP53 (R213Ter) showed somatic gene variations, and no exon amplification or deletion was detected in BRCA1/2.

Conclusions: Invasive carcinoma originating from microadenosis has the same immunophenotype as microadenosis, and its prognosis is difficult to determine.