For Information OnlyBreast
antigen retrieval protocol should be mentioned. The percentage of positive cells should also be mentioned when clinically relevant.
This protocol applies to all carcinomas of the breast. The World Health Organization (WHO) classification of breast carcinoma is presented below, although the protocol does not preclude the use of other classifications or histologic types, such as that published in the Armed Forces Institute of Pathology Fascicle on breast tumors.2,3
WHO Classification of Carcinoma of the Breast
Noninvasive carcinoma (NOS)
Ductal carcinoma in situ
Lobular carcinoma in situ
Invasive carcinoma (NOS)
Invasive ductal carcinoma
Invasive ductal carcinoma with an extensive intraductal component
Invasive ductal carcinoma with Paget disease
Carcinoma with metaplasia
Spindle cell type
Cartilaginous and osseous type
Inflammatory (largely clinically defined; see Note M)
# Classic invasive lobular carcinoma, which has a better prognosis than invasive carcinoma, NOS, is diagnosed only when the tumor exhibits a single file growth pattern, a monotonous population of small cells with very low grade nuclei, and low cell density. Tumors with a diffuse infiltrative growth pattern, which do not fulfill these criteria, should be reported by histologic grade with the suffix “with lobular features” (or “lobular variant”). Such tumors are separately identified because this growth pattern has been associated with extensive intramammary growth and distinctive patterns of metastasis.
## The diagnosis of pure mucinous carcinoma requires the presence of low-grade nuclei and extracellular mucin in at least 90% of the tumor. Tumors with less extensive mucin production should be classified as invasive ductal carcinoma with the suffix “with mucinous features” and graded.
### The diagnosis of medullary carcinoma requires strict adherence to diagnostic criteria: a sharply circumscribed tumor border; high histologic grade with patternless, syncytial sheets of large, undifferentiated tumor cells; a substantial and diffuse lymphoplasmacytic infiltrate between cellular nests; and scant fibrous stroma. Tumors lacking all of these