This article reports the case of a mixed metaplastic carcinoma with heterologous mesenchymal chondroid and spindle cell differentiation, Elston and Ellis grade III, triple negative phenotype, developed on atypical microglandular adenosis. It describes the diagnoses of microglandular adenosis, atypical microglandular adenosis and their differential diagnoses and reviews the cases of carcinomas developed on microglandular adenosis reported in the literature with their molecular biology analyses.