BREAST CYTOPATHOLOGY

130 4. Primary Malignant Tumors
Pitfalls and Differential Diagnosis
• An important differential diagnosis to consider is
a metastatic carcinoid or small cell carcinoma from
another site.
• Immunohistochemical stains, other than neuroendocrine
markers, may be utilized to distinguish between primary
neuroendocrine carcinoma and small cell carcinoma from
a metastatic tumor.
• In general, breast small cell carcinomas are CK-7 positive
and CK-20 negative, whereas lung small cell carcinomas
tend to be negative for CK7 and CK-20.
• In addition, estrogen and progesterone receptors and
GCDFP-15 are positive in the primary breast carcinomas.
• To distinguish breast small cell carcinoma from infiltrating
lobular carcinomas, E-cadherin may be of significant
value.
• A majority of small cell carcinomas will be E-cadherin
positive as compared with lobular carcinomas, which will
all be negative.
• The neuroendocrine nature of these tumors can be confirmed
by using neuroendocrine markers such as synaptophysin
and chromogranin.
Sweat Gland (or Salivary Gland-Type)
Tumors
Clinical Features
• These are rare skin neoplasms (approximately 1 in every
20,000 skin malignancies).
• They rarely occur in the breast.
• Among the sweat gland carcinomas, those of eccrine origin
are most common.
• Eccrine carcinomas may arise de novo from any portion
of the normal eccrine apparatus or may result from the
transformation of an existing benign eccrine tumor.
• Malignant hidradenoma is thought to originate from the
distal eccrine excretory duct.