Prognostic factors in primary mucinous breast carcinoma

Two hundred seven mucinous breast carcinomas were morphologically classified into two different groups: pure mucinous carcinomas consisting only of areas with small epithelial islands of solid tumor floating in abundant extracellular mucin, and mixed carcinomas where the tumor contains large areas of mucin, as well as areas with infiltrating carcinoma devoid of extracellular mucin. Of the 207 tumors, 95 were of the pure type and 112 of the mixed type. The pure and mixed carcinomas differed significantly with respect to a number of prognostic factors, the most important of which was lymph node status. Patients with pure mucinous carcinomas had significantly fewer lymph node metastases at the time of primary operation (P = 0.0001) and a significantly longer recurrence-free survival (P = 0.03) than patients with mixed carcinomas. Patients with mixed carcinomas closely resembled patients with infiltrating ductal carcinomas not otherwise specified (NOS) with respect to both lymph node status and recurrence-free survival. In multivariate analysis, the single most important factor for predicting recurrence-free survival among the 207 patients was lymph node status. However, of 94 pure carcinomas, only 6 had lymph node metastases at the time of mastectomy. A detailed morphologic analysis demonstrated that two of these six cases were incorrectly diagnosed as being pure mucinous carcinomas--they were actually of the mixed type. In another two of these cases, the metastases originated from a co-existent infiltrating ductal carcinoma. Thus, metastases to the regional lymph nodes were observed in only two cases of pure mucinous carcinomas. It is concluded that the biologic behavior of the pure mucinous carcinomas differs from that of both the mixed carcinomas and infiltrating ductal carcinomas NOS. Thus, a new definition is suggested, in which a mucinous carcinoma is classified as such only if it is a pure carcinoma, and mixed mucinous carcinomas are classified according to the component without extracellular mucin production.