BREAST CYTOPATHOLOGY

Special Types of Breast Carcinomas 105
panel of immunostaining for organ-specific antibodies are
the tools to distinguish between a primary signet ring carcinoma
and a metastatic tumor.
• The distinction between signet ring carcinoma and other
tumors requires special attention to subtle morphologic
differences.
• Infiltrating lobular carcinomas often show other characteristics
of this tumor, including (although rare), the presence
of the “Indian file” pattern. Secretory carcinomas present
with several prominent intracytoplasmic vacuoles.
• Lipid-rich carcinomas contain small cytoplasmic vacuoles
that present in different forms. The vacuoles are often
seen in the perinuclear area, and nuclei are indented.
Special stain demonstrates the presence of fat droplets in
the cytoplasm of tumor cells. These droplets are mucin
negative.
• Signet ring carcinomas must also be distinguished from
colloid/mucinous breast carcinomas because of the variability
in the clinical outcomes of these lesions. In signet
ring breast carcinomas, the mucin is present intracytoplasmically,
whereas in the colloid carcinomas, the tumor is
present as clusters of tumor cells in large mucin pools.
Invasive Micropapillary Carcinoma
Clinical Features
• Invasive micropapillary carcinoma is a rare variant of in -
filtrating ductal carcinoma first described by Siriaunkgul
and Tavassoli in 1993. It is characterized by the presence
of small clusters of tumor cells within artificially dilated
stromal spaces, the so-called morular or micropapillary
growth pattern. Also characteristic is the reverse cellular
polarity or the so-called inside-out appearance.
• This type is more frequently seen admixed with invasive
ductal carcinoma rather than in its pure form.
• These tumors account for less than 3% of all invasive breast
tumors.