Seborrheic Keratosis with Bowenoid Change
A seborrheic keratosis with bowenoid change is a rare malignant transformation where a benign seborrheic keratosis develops areas of squamous cell carcinoma in situ (Bowen disease) within the original lesion, characterized histologically by atypical keratinocytes with nuclear pleomorphism, abnormal mitoses, dyskeratotic cells, and clumping cells.
Pathologic Definition
This entity represents malignant transformation occurring within a pre-existing seborrheic keratosis rather than two separate colliding lesions 1, 2. The transformation is evidenced by:
- Contiguous zones showing gradual transition from benign SK to malignant areas 1, 3
- Intraepidermal nests containing atypical cells with features of Bowen disease
- Preservation of the underlying SK architecture in adjacent areas
Histopathologic Features
The bowenoid areas demonstrate:
- Nuclear pleomorphism and abnormal mitoses
- Dyskeratotic cells and clumping cells
- Bowenoid and pagetoid spreading patterns 2
- Increased p16, p21, and Ki-67 expression (typically >60%) 2, 4
- Strong p53 expression in malignant cells 4, 3
- Decreased cyclin D1 expression 4
The malignant components may histologically resemble porocarcinoma or inverted follicular keratosis 2.
Clinical Characteristics
This transformation occurs predominantly in elderly patients (median age 75 years) with large lesions 2:
- Lesions measuring >10-32 mm are at higher risk
- Can occur at any body site from scalp to lower extremities
- Patients may report a color change (development of pinkish or reddish areas within a brownish lesion) 5
- Immunosuppression is a significant risk factor 5
Association with HPV
HPV DNA has been detected in approximately 29% of cases (5 of 17 in one series), suggesting viral infection may contribute to malignant transformation in a subset of cases 4.
Clinical Significance
The key clinical pitfall is dismissing a changing seborrheic keratosis as benign. Any SK showing:
- Change in color (particularly development of erythematous areas)
- Rapid growth
- Ulceration or bleeding
- Size >10 mm in elderly or immunosuppressed patients
...warrants biopsy to exclude malignant transformation 2, 5.
Progression Potential
While most cases represent in situ carcinoma, invasive squamous cell carcinoma can develop, with documented cases showing in-transit skin metastasis 2. Loss of p16 expression correlates with progression from noninvasive to invasive carcinoma 2.