Porokeratosis is a rare keratinization disorder clinically characterized by annular brownish macules with an atrophic or depressed center and a raised, sharply marginated keratotic border, and histologically by a cornoid lamella. The ethiopathogenesis of this process is complex and multifactorial, and it is not clearly understood. It has been speculated that it comes from the proliferation of abnormal clones of epidermal keratinocytes, which may be triggered by several stimuli, such as sunlight exposure, radiation therapy, or immunosuppression, in genetically predisposed patients.
There are five main clinical variants of porokeratosis. The coexistence of porokeratosis and skin cancer is rare. The greatest risk is achieved in large and long duration lesions and in linear porokeratosis.
We report the case of a 59-year-old white, female, Fitzpatrick III skin phototype, with 18 years history of erythematous scaly papules on the upper and lower limbs. She denied immunosuppressive treatments and family history of porokeratosis. The diagnosis of disseminated superficial actinic porokeratosis (DSPA) was confirmed after clinical and histopathologic correlation. Since then, the patient was submitted periodically to cryotherapy, electrofulguration, and CO2 laser of lesions, with good cosmetic results. On the last visit, the patient reported a 4 months history of an irregular, hyperpigmented plaque on the right forearm [Figure 1]. We performed an excisional biopsy that showed an ulcerated superficial spreading malignant melanoma (4 mm of depth, Clark level IV, angioinvasion and neurotropism absent) with a cornoid lamella at the edge of the melanocytic tumor [Figure 2]. On the full-body computed tomography scan, there was no evidence of metastatic disease, and the patient was submitted to reexcision with 2 cm margins and sentinel lymph node biopsy, which was negative (Stage IIC).
The association of porokeratosis and malignant neoplasm is estimated between 6.9% and 11.6%. The most frequent tumors identified are “in situ” and invasive squamous cell carcinoma, and less-frequent basal cell carcinoma. The association with melanoma had been reported once by Maubec and colleagues.
P53 gene has a wide spectrum of mutations, which are present in half of all tumors. It has also been suggested that it is a major suppressing player in the progression from nevus to melanoma. In the lesions of porokeratosis, Magel et al. showed an overexpression of p53 in the nuclei of, mainly, basal keratinocytes within or under the cornoid lamella. The increase of p53 levels under the cornoid lamella could be associated with malignant transformation or it is only a protective reaction following intense UV exposure, as previously reported?
In our case, the intermittent but intense sun exposure reported by our patient, which is an isolated risk factor for malignant melanoma, may justify the appearance of a malignant melanoma as a random event in a patient with DSPA. However, the presence of a cornoid lamella adjacent to malignant melanoma may suggest that DSPA might be a cancer-prone condition.
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