BREAST CYTOPATHOLOGY

Lobular Carcinoma 99
pattern of metastatic presentation and tends to involve skeletal,
visceral, serosal, and meningeal areas. Similarly, ovary,
bone, and uterus are the common sites of metastasis from this
tumor.
Mammographically, it can present as an asymmetric density
with no clearly delineated margin with no or little architectural
distortion. A mass may be firm to hard or not readily
palpable or visible. The mass may be detected mammographically,
although microcalcifications are uncommon. Multifocal
infiltrating lobular carcinoma may present with minimal
distortion with no significant mass or increased density. These
subtle mammographic features warrant careful examination
of the breast and sampling of any suspicious area. Infiltrating
lobular carcinoma is often bilateral and shows evidence of
multicentricity.
Histologic Features
Pathologically, infiltrating lobular carcinoma is characterized
by diffuse infiltration of mammary stroma and ductal structures
by neoplastic cells in a pagetoid growth pattern. The
tumor may be difficult to define by gross examination because
of the diffuse nature of the malignancy. Areas of carcinoma
in situ are commonly seen. Histologic growth patterns of
lobular carcinoma include solid, alveolar, and the pleomorphic
variant.
This variety of patterns exhibits similar prognostic behavior
except the pleomorphic variant, which is associated with
a more unfavorable outcome. By immunohistochemistry, a
majority of the lobular carcinomas (up to 95%) are estrogen
receptor positive, while 60%–70% are progesterone receptor
positive. Immunohistochemical analysis has shown a complete
loss of E-cadherin expression in a majority of infiltrating
lobular carcinomas (80%–100%).
Cytomorphologic Characteristics (Figures 4.19 to 4.25)
• Lesions have variable cellularity, and smears are usually
hypercellular.
• Cells have small uniform nuclei and small nucleoli.