BREAST CYTOPATHOLOGY

118 4. Primary Malignant Tumors
Pitfalls and Differential Diagnosis
• Sometimes difficult to distinguish from cribriform carcinoma
of the breast
• Infiltrating lobular carcinoma
• Immunohistochemistry may be of some value in this distinction
because cribriform breast carcinoma is usually
estrogen and progesterone positive while adenoid cystic
carcinoma is estrogen and progesterone negative
• Other mimics may be collagenous spherulosis and pleomorphic
adenoma
Squamous Cell Carcinoma
Clinical Features
• This entity should include only lesions that are predominantly
squamous and not adenocarcinoma with squamous
metaplasia.
• No specific clinical features of squamous cell carcinoma
distinguish it from other subtypes.
• Squamous cell carcinoma may be a component of metaplastic
carcinoma or may exist as a pure form.
• Approximately 10%–15% of pure squamous cell carcinomas
have axillary node metastasis.
Cytomorphologic Characteristics (Figures 4.40 and 4.41)
• Cellular aspirate
• May be composed entirely of squamous cells, which are
keratinizing, nonkeratinizing, or spindled
• Background keratinous debris and extensive necrosis
• Cystic degeneration and hemorrhage
Pitfalls and Differential Diagnosis
• Cytologic appearance of the aspirate may be identical in
cases of primary breast squamous cell carcinoma versus
metastatic squamous cell carcinoma. Clinical history
plays a key role in the distinction of the former from the
latter.