[Pathologic diagnosis and differential diagnosis of low-grade adenosquamous carcinoma of breast and syringomatous adenoma of nipple].

Objective: To investigate the pathologic and immunohistochemical features, diagnosis and differential diagnosis of low-grade adenosquamous carcinoma of the breast and syringomatous adenoma of the nipple.

Methods: Six cases of low-grade adenosquamous carcinoma of the breast and four cases of syringomatous adenoma of the nipple were examined histologically and immunohistochemically (MaxVision method), and the literature was reviewed.

Results: The two types of tumors were similar in morphology, but located in different regions with low-grade adenosquamous carcinoma being present in the deep parenchyma and syringomatous adenoma in nipple. Both types of tumors were composed mainly of well-differentiated glands with angulated, comma shaped or polliwog appearance in a disordered infiltrative pattern. The tumor cells also formed solid tubules, strips or nests, with frequent areas of squamoid differentiation. Mitosis was rare. The interstitial tissue showed abundant spindle cells or sclerotic fibrosis with mixed inflammatory cells infiltration. One case of low-grade adenosquamous carcinoma showed a concomitant malignant adenomyoepithelioma, and another case showed concomitant spindle cell metaplastic carcinoma. One case of syringomatous adenoma involved the deep parenchyma. Immunohistochemistry of low-grade adenosquamous carcinoma showed that CK5/6 and p63 were positive in the outer layer of the glands and the squamoid epithelium, and CD10 was also positive in the outer layer of the glands. ER and HER2 were negative, and PR was also negative except for one case in which the spindle cells were positive for CK5/6, AE1/AE3 and PR focally. Immunostaining of syringomatous adenoma demonstrated that p63 and CK5/6 were positive in the outer layer of the glands and the squamoid epithelium. Calponin, SMA, ER, PR and HER2 were all negative.

Conclusions: Low-grade adenosquamous carcinoma of the breast and syringomatous adenoma of the nipple are similar in morphology and immunohistochemical phenotype, while the biological features are opposite due to different locations. The differential diagnoses include tubular carcinoma, adenosquamous carcinoma, radial sclerosing lesions and others.