Squamous Cell Carcinoma in-situ and Basal Cell Carcinoma Arising From Seborrheic Keratosis in the Same Patient.

Sir,

Seborrheic keratosis (SK) is a common benign tumor in which malignancies like melanoma and nonmelanoma skin cancers (NMSCs) can arise rarely. Herein, we report an unusual case of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) in-situ arising from SKs in the same patient. To our knowledge, this is the first report of such malignant transformation in type V-VI skin.

A 65-year-old man presented with a pigmented growth over chest and left thigh for 20 years. Six months ago, he had noticed pain with ulceration and serosanguinous discharge from the lesion over left thigh. Three months later, the chest lesion developed similar changes. On examination, a 6 cm × 4 cm hyperpigmented, verrucous plaque was seen over the anterior aspect of left thigh. The base was indurated, and the margins showed crusting and scaling [Figure 1]. Over the chest, a 2 cm × 2 cm similar plaque was seen. The right side of the lesion was ulcerated with bleeding, crusting and rolled out margin [Figure 2]. An incisional biopsy was done from both the lesions.

Figure 1

Seborrheic keratosis over left thigh showing indurated base with crusting and scaling of margins

Figure 2

Seborrheic keratosis over chest with one area showing rolled out margins, ulceration, bleeding and crusting

Histopathology from the plaque over thigh revealed irregularly thickened epidermis with full thickness dysplasia, intact basement membrane, large hyperchromatic nuclei, increased nuclear: Cytoplasmic ratio, abnormal mitoses and nuclear pleomorphism [Figure 3]. Histopathology of the chest plaque revealed irregular proliferation of basaloid cells with peripheral palisading and clefting between epithelium and surrounding stroma [Figure 4]. The cells showed predominantly adenoid pattern with few areas of melanin deposition [Figure 5]. In addition, both the sections showed presence of horn cysts in the vicinity of the tumor, suggestive of SK (arrows). Based on this, a diagnosis of SCC in-situ and BCC (adenoid type) arising in SKs was made. The patient underwent wide local excision of the lesions and is currently asymptomatic.

Figure 3

Horn cyst (arrow) with full thickness epidermal dysplasia, disorderly arrangement of cells, large hyperchromatic nuclei, pleomorphism, increased nuclear: Cytoplasmic ratio and abnormal mitoses – consistent with squamous cell carcinoma in-situ (H and E, original magnification × 100)

Figure 4

Horn cyst (arrow) with irregular proliferation of basaloid cells, peripheral palisading and clefting between epithelium and surrounding stroma – consistent with basal cell carcinoma, (H and E, original magnification × 40)

Figure 5

Adenoid pattern of basal cell carcinoma with occasional melanin pigment deposition, (H and E, original magnification × 100)

Seborrheic keratosis is one of the most common benign skin tumors in the elderly. Malignant transformation, though uncommon, is known to occur in skin types I-III. The incidence of this varies from 0.14% to 7%, with higher frequencies being found in those studies where only the clinically suspicious lesions were biopsied.[1234] The most common type of malignancy arising in SK is variably reported as BCC,[145] SCC in-situ[3] and invasive SCC.[2] Keratoacanthoma, malignant melanoma, and trichilemmal carcinoma have also been described.[56] The most common histological subtype of SK in which malignancies arise is acanthotic type and the most common type of BCC seen is superficial spreading type.[2]

Malignant transformation is usually seen in males above 50 years of age. Head, neck and back are more often affected, where there is a greater degree of solar damage.[4] The contribution of SK towards the development of the tumor is debatable, with many authors calling it a matter of chance. Some have found tumor cells contiguous with the SK, whereas others have found them lying adjacent but separately from each other, calling it “collision tumor” or “compound tumor.”[3] Cascajo et al. opined that the different skin cancers associated with SKs developed from the three different types of cells that constituted SKs, that is, BCC develops from basaloid cells, SCC from the spinous cells, and malignant melanoma from melanocytes.[5]

An earlier report of two separate lesions of Bowen's disease arising from SK over two different locations (bilateral pretibial) in the same patient proposed that carcinomatous changes can affect several SK lesions in the same patient.[7] A retrospective study at a referral center found that almost 20% of the patients referred for Moh's surgery had multiple synchronous NMSCs, and another 20% developed metachronous lesions over a period of next 2 years.[8] Increasing age and immunosuppression are common reasons for developing multiple primary skin cancers. However, to our knowledge, this is the first report of 2 different NMSCs developing simultaneously in SK at two different sites in the same patient having type V-VI skin. Furthermore, our patient had adenoid type of BCC, which, to our knowledge, has previously not been described as arising out of SK.

This report underscores the importance of low threshold for biopsy of suspicious lesions of SK in the presence of danger signs such as erythema, ulceration, bleeding and crusting as they may herald malignant transformation.