Seborrheic keratoses (SKs) are the most common benign epidermal tumor of the skin commonly arising in middle-aged individuals. Genetics, sun exposure, and infection have all been implicated as possible factors. Males and females are equally affected and there is little tendency to spontaneous disappearance. Usually they run a benign course but rarely malignancies like basal cell carcinoma (BCC), melanoma and nonmelanoma skin cancers can arise [1,2]. Keratoacanthoma, malignant melanoma, and trichilemmal carcinoma have also been described [2,3]. Herein, we report a case of squamous cell carcinoma arising over a long-standing seborrhoeic keratosis in 70-year old male, which was managed with a wide surgical resection.

A 70-year-old man presented with history of a pigmented growth over pubic region for the last 25 years. Over the last one year, there was development of a protuberant mass over the lesion. The mass was gradually progressive and was associated with pain, ulceration and serosanguinous discharge. The patient was a known diabetic and hypertensive and gave history of significant weight loss over the last one year. On examination, a well defined exophytic mass, around 3 cm in diameter, was present over the pubic area. The surface of the lesion was ulcerated with fissuring and examination of the base revealed a hyperpigmented plaque of size 1 cm from which the lesion appeared to be arising (Fig. 1). Systemic examination revealed inguinal lymphadenopathy. The patient was advised complete excision of the lesion which was later on performed by a surgeon and the lesion was subjected to histopathological examination. Histopathology of the lesion revealed thickened epidermis with full thickness dysplasia, hyperchromatic nuclei, abnormal mitoses with areas of maturation forming parakeratotic horny pearls and individually keratinized cells, confirming the diagnosis of squamous cell carcinoma (Fig. 2).

The patient was asymptomatic after surgical excision and there was no recurrence of the lesion after six months of follow-up.

SKs are the most common benign tumors of the skin, commonly seen among the elderly and the middle-aged. The higher prevalence of SKs on sun-exposed skin implies a possible causative role of sunexposure. SKs have also been found to demonstrate irregularities in the expression of the apoptosis markers p53 and Bcl-2, but so far no genetic locus or chromosomal imbalance has been detected. Usually SKs have a benign course but varying degrees of squamous atypia have been seen [2]. 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 [2-4]. Although it is likely that most of these lesions represent collision tumors, malignant transformation of SKs into basal cell carcinomas, squamous cell carcinomas, and melanomas can occur rarely. The most common type of malignancy arising in SK is variably reported as BCC, squamous cell carcinoma (SCC) in-situ and invasive SCC. Keratoacanthoma, malignant melanoma, and trichilemmal carcinoma have also been described to arise over SKs [2,3].

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 [4]. In some cases, histology of the lesion shows tumor cells lying adjacent but separately from SK cells, which is termed as a “Collision tumor” or a “Compound tumor” [1]. Malignant transformation in SKs is usually seen among the elderly over the photoexposed sites like head and neck. It has been postulated that different 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 [3].

This report highlights the rare but potentially life threatening risk of malignant transformation of SKs and the dermatologists should be well aware of the risk and timely biopsy of suspicious lesions of SK should be performed as they may mark the onset of malignant transformation.