OBJECTIVETo study the clinicopathologic features and immunophenotype of solid papillary carcinoma (SPC) of breast.

METHODSClinical and pathologic features of 21 cases of SPC, with or without stromal invasion, were analyzed. Immunohistochemical study (LSAB method, for cytokeratins, myoepithelial markers, chromogranin A, synaptophysin, Ki-67, estrogen receptor, progesterone receptor, c-erbB-2 and pS2) and alcian blue staining were performed.

RESULTSAll the patients were females with a mean age of 66.1 years. The clinical features were similar to those of classic papillary tumor. Metastasis was not observed in patients who had undergone axillary lymph node dissection. Histologically, the tumor displayed solid papillary growth pattern, with mucin production demonstrated in 19 cases. The tumor cells were oval, polygonal, spindled or signet ring-like and contained mildly to moderately pleomorphic nuclei. The mitotic count measured less than 5 per 10 high-power fields in 15 cases. Seven cases contained foci of invasive carcinoma which showed similar cytologic features as those of the in-situ component. Immunohistochemical study showed that the tumor cells expressed CK8 but not basal cell cytokeratin. Positivity for smooth muscle actin-alpha, calponin and p63 was demonstrated in the myoepithelial layers of fibrovascular cores, as well as around the expanded ductolobular units. Most cases also showed cytoplasmic positivity for chromogranin A (88.2%) and synaptophysin (82.4%). The proliferation index, as highlighted by Ki-67 immunostain, was 8.1%. The tumor expressed estrogen receptor, progesterone receptor and pS2. The staining for c-erbB-2 oncoprotein was negative. Follow up of 16 patients showed no evidence of recurrence or metastasis.

CONCLUSIONSSPC predominantly affects elderly females and has distinctive pathologic features and immunophenotype. Some cases of SPC are associated with mucinous and neuroendocrine components. Follow-up data suggest that SPC often carries an indolent clinical behavior and favorable prognosis.