TEACHING CASE
Solid variant of mammary “adenoid cystic carcinoma with basaloid features” merging with “small cell carcinoma”

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Abstract

We describe a rare case of a solid variant of a mammary adenoid cystic carcinoma with basaloid features (sbACC) and its coexistence with a “small cell” carcinoma (SCC), identified and confirmed by histological and immunohistochemical observations: the absence of glandular structures and PAS-positive globules, positivity for neuroendocrine markers (NSE, synaptophysin and chromogranin), and negativity for 34betaE12 and SMA actin were the aspects suggesting the presence of SCC.

Furthermore, positivity for CD10 was found both in sbACC and in SCC, supporting the hypothesis that the two components share the same histogenetic myoepithelial origin and represent an example of dedifferentiation along neuroendocrine phenotype lines occurring in a multipotential neoplastic stem line, already committed towards a myoepithelial phenotype.

To our knowledge, this is the first reported case of a solid basaloid adenoid cystic carcinoma merging with an SCC carcinoma. Furthermore, it is the first study in which CD10 was used to investigate the histogenesis of the two neoplastic components.

Introduction

Adenoid cystic carcinoma (ACC) of the breast is a rare neoplasm (<1% of breast carcinomas) with an excellent prognosis. As in salivary glands, a variety of microscopic growth patterns (cribriform, glandular, trabecular, solid, and basaloid) have been described in the breast. It has been reported that solid and basaloid variants are associated with a more aggressive clinical course [2], [8], [9] and have been considered as” high grade” tumors. Recently, Shin and Rosen [11] have described a series of nine cases of a rare subtype of “solid adenoid cystic carcinoma with basaloid features”(sbACC) in the breast, reporting on a differential diagnosis from other neoplasias, including primary small cell carcinoma (SCC) of the breast. This study describes a very rare case of mammary neoplasia in which solid, basaloid adenoid cystic areas (sbACC) merge with more extensive areas of primary “SCC”.

Since these two neoplastic histotypes are very rare in the breast, their histological and immunohistochemical features have been studied to provide a pathogenetic explanation for their coexistence in the same neoplasia.

Section snippets

Case report

A 40-year-old woman, with type I diabetes mellitus, no risk factors for oncological disease, presented a nodule (about 2 cm) discovered in the central quadrant in the retro-areolar zone of the left breast 4 months previously.

Clinical examination showed that the nodule was circular, with indistinct limits, subcutaneously mobile, but partly attached to the underlying glandular layer. No alterations of the areola or nipple were observed. Palpation of the left armpit identified a mobile, non-painful

Discussion

Mammary ACC is a tumor with a good prognosis and is histologically indistinguishable from ACC arising from other sites. As in the salivary glands, a variety of microscopic growth patterns (cribriform, glandular, trabecular, solid, and basaloid) have been described in the breast.

The solid and basaloid variants have been reported to be associated with a more aggressive clinical course [2], [8], [9] and have been considered “high grade” tumors.

The “sbACC” is a rare subtype of ACC, described by

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