BREAST CYTOPATHOLOGY

Special Types of Breast Carcinomas 103
• Predominant pattern is that of dissociation; “Indian file”
appearance is rarely appreciated in smears.
• Lesions may have little or no atypia.
• Nuclei are eccentric, with occasional intracytoplasmic
lumina with mucin droplets and rare signet ring cells.
• Monomorphic pattern of small cells arranged as single
cells, cords, or clusters with no recognizable myoepithelial
cells are the key features to differentiate infiltrating lobular
carcinoma from benign breast lesions.
• The pleomorphic variant features more pleomorphism and
nuclear atypia.
Pitfalls and Differential Diagnosis
Infiltrating lobular carcinoma is one of the main causes of a
false-negative diagnosis in breast FNA. This is often due to
the minimal atypia associated with this entity.
Differentiation between infiltrating lobular carcinoma
versus other entities may be difficult. Especially if the sample
is a hypocellular specimen, it is best to consider surgical excision
for further characterization of suspicious cells for lobular
carcinoma. There are overlapping features among atypical
lobular hyperplasia, lobular carcinoma in situ, and an in -
filtrating lobular carcinoma. These entities are collectively
called lobular neoplasia if the distinction is not possible.
Higher cellularity and a higher proportion of dissociated
cells are commonly seen in an infiltrating lobular carcinoma.
Differential diagnosis also includes other low nuclear grade
carcinomas of ductal origin. Immunostain for E-cadherin can
differentiate between these two entities.
Special Types of Breast Carcinomas
Signet Ring Carcinoma
Clinical Features
• These rare breast tumors are associated with an unfavorable
prognosis.