MUC5AC and neuroendocrine carcinoma: PMBCs are a heterogeneous group of tumors and can be further classified into two main subtypes by microscopic features of architecture and cytology: the “classical” variant, Type A (or paucicellular), with large quantities of extracellular mucin, and Type B (or hypercellular) tumors, which contain less mucin and often show histologic features significantly overlapping with those of neuroendocrine carcinomas (6, 7).