Case Three – March 2017
- 68 year old male presented with a 3 cm mass on the right scalp
- No evidence of ulceration or epidermal change was seen
- Pilar cyst
- Lipoma
There is a complex, solid and cystic squamous proliferation present entirely within the dermis without an epidermal connection.
The undulating squamous epithelium shows evidence of trichilemmal differentiation with absence of a granular cell layer and presence of dense keratin.
The squamous cells are mitotically active and exhibit cytologic atypia with nuclear pleomorphism and hyperchromasia.
Differential Diagnosis:
- Trichilemmal carcinoma
- Squamous cell carcinoma with trichilemmal differentiation
- Pilar cyst
- Malignant proliferating pilar tumor
Malignant proliferating pilar tumor
- Rare malignant squamous neoplasm that represents malignant transformation from a pre-existing pilar/trichilemmal cyst
- Most often presents as a nodule on the scalp of women during the fourth to eighth decades of life
- These tumors exhibit increased complexity compared to a pilar cyst with solid and cystic areas, nuclear atypia, and an infiltrative growth pattern
- Due to the presence of cytologic atypia and solid areas with an infiltrative growth pattern, malignant proliferating pilar tumors mimic cutaneous squamous cell carcinoma histopathologically
- Primary squamous cell carcinoma should demonstrate connection to the overlying epidermis and often also show an overlying in situ component
- Malignant proliferating pilar tumors are positive by immunohistochemistry for CD34, which is a marker for trichilemmal differentiation
- Cutaneous squamous cell carcinoma is typically negative for CD34
- The histologic differential diagnosis also includes trichilemmal carcinoma, which a malignant neoplasm arising from a trichilemmoma
- Often presents on the face and ears
- Positive for CD34 immunohistochemical stain
- Malignant proliferating pilar tumors may potentially recur locally or regionally
- Regional metastasis also has been reported
- Wide local excision is the treatment of choice for malignant proliferating pilar tumors to ensure complete removal and to prevent recurrence
- Malignant proliferating pilar tumors are malignant squamous neoplasms with trichilemmal differentiation that arise from a pre-existing pilar/trichilemmal cyst
- Malignant proliferating pilar tumors mimic cutaneous squamous cell carcinoma and trichilemmal carcinoma histopathologically
- Although arising from a pre-existing pilar/trichilemmal cyst, malignant proliferating pilar tumors can locally recur and rarely metastasize to lymph nodes
- Wide local excision is the treatment of choice to prevent local recurrence