BREAST CYTOPATHOLOGY

104 4. Primary Malignant Tumors
• They represent 2%–4% of all breast carcinomas.
• Lesions occur in patients older than the average age of
patients with ordinary breast carcinoma.
• The usual age is in the mid to late fifties.
• Signet ring cell carcinomas tend to be more aggressive than
mucinous/colloid, ductal, and lobular carcinomas.
• Signet ring cell carcinomas tend to involve metastatic sites
such as serosal surfaces of the stomach, female genital
tract, and urinary tract.
• They tend to have a high incidence of lymph node involvement
and advanced stage of presentation. The prognosis is
usually poor.
• The origin of this as a variant of mucinous carcinoma versus
an infiltrating lobular carcinoma remains controversial,
and many cases cited in the literature have been classified
as a variant of infiltrating lobular carcinoma.
• These tumors must be distinguished from duct-derived
tumors such as colloid and mucinous carcinomas.
Cytomorphologic Characteristics
• The tumor is characterized by infiltration of breast stroma
by signet ring cells with an obvious intracellular mucin
accumulation.
• Tumors may present with moderate to rich cellularity.
• The cells are arranged singly and in small, loose clusters.
• The cells are small with crescent-shaped nuclei compressed
to the cell periphery by mucin.
• The mucin is mucicarmine and periodic acid–Schiff positive
and is packed in a cytoplasmic vacuole.
Pitfalls and Differential Diagnosis
• The differential diagnosis includes metastatic carcinoma,
especially from gastrointestinal tumors, infiltrating lobular
carcinomas, secretory carcinomas, and lipid-secreting
carcinomas.
• Clinical history, the original pathology slides, and ancillary
studies such as special stains, electron microscopy, and a