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invasive ductal starting in milk duct |
invasive lobular starting in lobule |
| Infiltrating ductal carcinoma is by far the most common histologic type
(accounting for approximately 75 percent of breast cancers) and is characterized by the
absence of any special histologic features. These tumors commonly metastasize to the
axillary lymph nodes, and their prognosis is poorer than that for the special histologic
types. Infiltrating lobular carcinoma is relatively uncommon, accounting for only 5 to 10 percent of breast tumors in most series. The typical clinical finding at presentation is an area of ill-defined thickening in the breast, in contrast to the prominent lump characteristic of ductal carcinoma. Lobular carcinomas are also characterized by a greater proportion of multicentric tumors, either in the same or the opposite breast, as compared with infiltrating ductal carcinoma. Overall, infiltrating lobular carcinoma and infiltrating ductal carcinoma have similar likelihoods of axillary-node involvement and similar prognoses. However, the sites of metastases of these two types tend to differ. Ductal carcinomas more frequently metastasize to bone or to intraparenchymal sites within the lung, liver, or brain, whereas lobular carcinomas more often metastasize to meningeal and serosal surfaces and other unusual sites. The three most common special types of invasive breast cancer are tubular, medullary, and mucinous. Tubular carcinoma is a type of carcinoma in which tubule formation is conspicuous. Generally, this diagnosis is made only when 75 percent or more of the tumor is composed of these elements. Tubular carcinoma constitutes about 2 percent of all breast cancers. Axillary metastases are uncommon, and the prognosis is considerably better than for infiltrating ductal carcinoma. Medullary carcinoma is a grossly well circumscribed lesion that is characterized microscopically by poorly differentiated nuclei, a syncytial growth pattern, a well-circumscribed border, intense infiltration with small lymphocytes and plasma cells, and little or no associated ductal carcinoma in situ. It accounts for 5 to 7 percent of all breast carcinomas. The five-year survival rate after treatment for medullary carcinoma is better than for infiltrating ductal carcinomas. Mucinous (or colloid) carcinoma constitutes about 3 percent of all mammary carcinomas and is characterized by the abundant accumulation of extracellular mucin around clusters of tumor cells. It is slow growing and can become bulky. When the tumor is predominantly mucinous, the prognosis tends to be favorable. Other, rarer, special types of carcinomas include papillary, apocrine, secretory, and metaplastic carcinomas (including squamous-cell carcinomas, spindle-cell carcinomas, and carcinosarcomas). In some cases, infiltrating ductal carcinomas include small areas containing these special types. |
