A morphological and immunohistochemical study of ductal carcinoma in situ, invasive breast carcinoma of no special type, and mucinous carcinoma of the breast in comparison with solid papillary carcinoma regarding neuroendocrine marker expression.

The exact relationship between solid papillary carcinoma (SPC) and invasive breast carcinoma of no special type (IBC-NST) with neuroendocrine differentiation and SPC and mucinous carcinoma (MC) of the breast remains unclear. To clarify the relationship, we conducted a comparative study of morphological and neuroendocrine features between ductal carcinoma in situ (DCIS, 72 cases) and SPC in situ (35 cases), and IBC-NST (103 cases) and invasive SPC (92 cases). We also conducted the study between MC associated with and without SPC. Synaptophysin, chromogranin A, and INSM1 were employed for the immunohistochemical study. IBC-NST had occasionally a morphological similarity with invasive SPC. While 123 of 127 cases with SPC demonstrated diffuse staining with one or more of the neuroendocrine markers, the only one case of DCIS and none of IBC-NST showed it. Type B was observed in 16 of 18 cases of MC associated with SPC and in 13 of 33 cases of MC without it. All the cases of MC with SPC and 6 of 33 cases without it showed diffuse staining for at least one of the neuroendocrine markers. In conclusion, a careful distinction between invasive SPC and IBC-NST with neuroendocrine differentiation is required. We assume that SPC in situ is a potential candidate for precursor of IBC-NST with neuroendocrine differentiation. MC of the breast is suggested to have two pathogenetic pathways through SPC in situ or non-SPC in situ. SPC in situ is thought to be less common as a precursor of MC than non-SPC in situ.

Cytological study of 44 cases with solid papillary carcinoma and a systemic review of solid papillary carcinoma and neuroendocrine tumor of the breast.

BACKGROUND: Solid-papillary carcinoma (SPC) of the breast is a rare variant of low-grade in situ and invasive carcinoma but there are only a few of the cytologic studies. METHODS: We examined 44 cases of SPC of the breast to define the cytologic features. We also made a systemic review of reported cases of SPC and neuroendocrine tumor (NET) of the breast. RESULTS: Both of our and the reviewed cases with SPC were very similar in the cytologic finding. It included hypercellularity, highly discohesive clusters, numerous isolated cells, small nuclei, finely granular chromatin of salt-and-pepper appearance, inconspicuous nucleoli, low nuclear-cytoplasmic ratio, and a plasmacytoid appearance. Moreover, SPC and NET had frequently all of these features in common. Capillary vessels structures and mucinous substance were not frequently seen in our and the reviewed cases with SPC. Rosette and pseudorosette were very rare in the cytologic specimen. The immunocytochemistry with our 9 cases with SPC indicated diffuse positivity for chromogranin A and/or synaptophysin. CONCLUSION: Many cytologic features are frequently shared by SPC and NET of the breast. However, the vascular structure may not be a precise criterion for SPC. Rosette and pseudorosette are rarely helpful for the cytologic diagnosis.