Our experience with 24 patients diagnosed as mucinous carcinoma of the breast between 1975 and 1995 was reviewed. All patients were females of 27 to 69 years old with an average of 59 6. Histologic types were divided into pure (20 cases) and mixed form (4 cases) according to the criteria of capella. Immunohistochemistry determine proliferating cell nuclear antigen (PCNA) was used. The PCNA scores were varied with the histologic grade of the tumor:Grade Ⅰ (5 casses): 0-25%; Grade Ⅱ(13 cases): 26-50%; Grade Ⅲ(5 cases):51-75%; and Grade Ⅳ(1 cases);>76%

Mitotic figures were rare (0-5/10HPF). Based on the intensive PAS

AB (ph2 5) and toluidine blue positivity

the mucin was interpreted as sialic acid mixed with neutral mucopolyasccharide. By the Grimlius stain

9 cases were argyrophilic. Ultrastructural examination of 4 cases showed acitve secreting epithelial cells with abundant surface microvelli. There were pools of extracellular mucin in the stroma. Distinct neurosecretory granules were identified in two cases. This research supports that not all but some of the mucinors carcinomas show neuroendocrine differentiation and therefore mucinous carcinomas of the breast are a heterogeneous guoup of tumosrs.