INTRADUCTAL AND LOBULAR ADENOCARCINOMA
The two main types of breast adenocarcinomas are ductal carcinomas (85%) and lobular carcinomas. Based on the tumor’s histology, these are also sometimes classed as papillary adenocarcinomas; carcinomas with gelatinous, mucoid degeneration; or as a kind of intraductal carcinoma that forms plugs in preexisting ducts and circumscribed rings of carcinoma cells. These forms of circumscribed adenocarcinomas bulge out-wardly from the chest wall rather than retract inwardly as in the inﬁltrating form. Skin adherence or ulceration and axillary node involvement occur much later in the course of the disease than in the ordinary scirrhous form. The tumors progress slowly to an immense size. The most common type of adenocarcinoma is ductal carcinoma, which begins in the cells of the ducts. Lobular carcinoma begins in the lobes or lobules and is more often found bilaterally than are other types of breast cancer. The cancer is classiﬁed based on the predominant histologic cells; however, several cellular patterns may be found in any one tumor.
In intraductal carcinoma in situ,
the cellular abnormalities are limited to the ductal epithelium and have not
penetrated the basement membrane of the duct. It is most common in
perimenopausal and postmenopausal women. Because the disease does not produce a
deﬁnitive mass, intraductal carcinoma in situ is not usually detected by
palpation. The histologic diagnosis of intraductal carcinoma in situ includes a
heterogeneous group of tumors with varying malignant potential. Carcinoma
develops in approximately 35% of women with this disease within 10 years of
initial diagnosis, and 5% to 10% of women will have a simultaneous invasive
carcinoma in the same breast at the time of biopsy.
Unlike intraductal carcinoma in
situ, lobular carcinoma in situ should not be treated as a cancer or cancer
precursor but rather as a marker for an increased breast cancer risk. It has a
much greater tendency to be bilateral and to present as multifocal disease.
Three of four patients with lobular carcinoma in situ are in the pre-menopausal
age group. The latent period to the development of invasive carcinoma is longer
than with intraductal carcinoma in situ; often more than 20 years will elapse
before inﬁltrating carcinoma develops. Approximately 20% of women with this
disease eventually develop invasive breast carcinoma. Paradoxically, most of
these subsequent carcinomas are ductal, not lobular.
In cases of inﬁltrating ductal
carcinoma, nonuniform malignant epithelial cells of varying sizes and shapes
inﬁltrate the surrounding tissue. The degree of ﬁbrous response to the invading
epithelial cells determines the ﬁrmness to palpation and texture during biopsy.
Often the stromal reaction may be extensive. Approximately 10% of inﬁltrating
ductal carcinomas are of a uniform histologic picture and are classiﬁed as
medullary, colloid, comedo, tubular, or papillary carcinomas. In general, the
specialized forms are grossly softer, mobile, and well delineated. They are
usually smaller and have a more optimistic prognosis than the more common
heterogeneous variety. Medullary carcinomas are soft, with extensive stromal
inﬁltration by lymphocytes and plasma cells.
Colloid or gelatinous carcinomas have a similar soft consistency, with
extensive deposition of extracellular mucin.
Inﬁltrating lobular carcinomas are
histologically notable for the uniformity of the small, round neoplastic cells.
Histologic subdivisions of inﬁltrating lobular carcinoma include small cell,
round cell, and signet cell carcinomas. Often the malignant epithelial cells
inﬁltrate the stroma in a single ﬁle fashion. This cancer tends to have a
multicentric origin in the same breast and to involve
both breasts more often than inﬁltrating ductal carcinoma. On palpation, these
growths feel boggy and semimovable and are dependent and heavy when the breast
is moved upward. The papillary carcinomas may contain a cystic cavity with
blood. The intraductal carcinomas form plugs (comedones), which may be
expressed from the ducts. On cross section the gelatinous carcinomas contain a
characteristic slimy, gray, mucoid material that spills from the tumor, which is honeycombed with this substance.