At present the diagnosis of BNEC

At present the diagnosis of BNEC requires expression of neuroendocrine markers in > 50% of the cell population, and the expression should be positive for at least two of the following markers: chromogranin A, synaptophysin, CD56 (NCAM) and NSE. Our case had IHC expression in 100% of NSE, 80% of synaptophysin and 60% of chromogranin A, correlated with the definition of BNEC. A breast tumor with focal and scattered IHC NE staining should be regarded as a tumor with endocrine differentiation, but not a BNEC. Both the ER and PR expressions of our case were similar to those of most well differentiated BNECs, which indicates a good prognosis. Morphologically, most helpful diagnostic features of a solid BNEC are nuclear palisading, rosette formation, cellular monotony and presence of an intraductal carcinoma in situ component. The presence of intracellular or extracellular mucin, or both, in tumor kainate receptors could also be features of mucinous BNEC. However, most solid BNECs lack those specific features and might histologically overlap with conventional types of breast carcinoma. It is noticeable that only three of nine BNEC cases with features of invasive breast carcinoma, revealed those unique NE histological features in a study by Cai and Seng. Our case demonstrated no specific NE histological features, except for a marked crush artifact in the frozen section, which disappeared in the permanent section. The cellular monotony and rare mitoses also should provoke suspicion of a NE tumor. The crush artifact can occur in both low-grade and high-grade NE neoplasms. A crush artifact found in either the frozen section, cytology preparation or permanent sections of breast tumor should alert one to be the possibility of BNEC tumor. Most patients cited in literature concerning BNEC are women in the 6th and 7th decades of life. The mean age of BNEC is 66 years (range: 35–97 years) in a series of 38 cases studied by Upalakalin et al and 66.5 years (range: 43–79 years) in a series of 13 cases studied by Cai and Seng. Although the mean age is in the 7th decade, the disease may occur in the younger age group. Several case reports of solid BNEC, including ours, contain patients of a younger age, e.g., 46 years, 41 years, 34 years and 40 years. This might indicate that solid BNEC could occur at a much younger age. The percentages of BNEC among breast cancers are variable. Lopez-Bonet et al found only 7 BNEC cases in 1368 breast cancers (0.5%), screening first for neuroendocrine histological features, then with IHC stains for proof. Righi et al estimated BNEC to constitute about 1% of all breast carcinomas. Cai and Seng performed a screening test with IHC in all 410 breast cancers and found 13 BNECs (3.2%). Recognition of the variable histological expressions and wide application of IHC could improve the diagnosis of BNEC. Overall, BNECs, especially of the solid type, show a less aggressive clinical behavior when compared with unselected breast cancers. The prognosis of BNEC depends on the stage, tumor size and lymph node status, similar in patterns to those of usual breast cancer. It may become necessary to distinguish BNEC from conventional breast cancer. As there has only been one previous case report of mucinous BNEC in Taiwan, the incidence of BNEC seems to be greatly underestimated on this island.