An irregular pigmented lesion on the back.

The patient

An 87-year-old woman with a history of multiple basal cell carcinomas presented to a follow-up visit referring a pigmented, slowly growing lesion on her right scapula that had been present for one year. Physical examination revealed an irregular 12 × 5 mm well circumscribed pigmented lesion with an elevated keratotic surface (Figure 1).

Figure 1

Close up-view of the scapular area shows an irregularly pigmented lesion with a verrucous surface. [Copyright: ©2016 Gonzalez-Olivares et al.]

The dermoscopic evaluation revealed a multicomponent pattern: many colors, superior irregular pigmented network with blue-white veil and inferior cerebriform pattern surrounded by atypical pigmented network with sharp demarcation (Figure 2).

Figure 2

Dermoscopic features. Multicomponent pattern. [Copyright: ©2016 Gonzalez-Olivares et al.]

The patient underwent complete exeresis of the lesion and the specimen was stained with hematoxylin-eosin. Histopathological examination showed a papillomatous epidermal hyperplasia with hyperkeratosis and cell nests in the dermoepidermal junction (Figure 3) and proliferation of atypical intraepidermal melanocytes with a pagetoid spread (Figure 4).

Figure 3

Papillomatous epidermal hyperplasia with hyperkeratosis and cell nests in the dermoepidermal junction. Hematoxylin-eosin-stained section of the specimen (original magnification, 40x). [Copyright: ©2016 Gonzalez-Olivares et al.]

Figure 4

Proliferation of atypical intraepidermal melanocytes with a pagetoid spread. Note large epithelioid cells with nuclear atypia and abundant cytoplasm. Hematoxylin-eosin-stained section of the specimen (original magnification, 200x). [Copyright: ©2016 Gonzalez-Olivares et al.]

What is your diagnosis?

Diagnosis

Melanoma in situ arising in a seborrheic keratosis

Answer and explanation

Although previously reported, the presence of a malignant melanoma within a seborrheic keratosis is extremely rare [1,2]. Seborrheic keratoses are common non-melanocytic epidermal tumors that are usually well recognized clinically. Despite this, an accurate diagnosis may be troublesome at times. Dermoscopy is a non-invasive method and diagnostic aid and should be performed in all lesions [3].

In addition to melanocytic nevi, malignant neoplasms arising within or adjacent to seborrheic keratoses have been previously documented [1,2,4-7]. Cascajo et al performed a retrospective analysis of 54 malignant neoplasms in conjunction with seborrheic keratoses, most of them corresponding to basal cell carcinomas, followed in number by squamous cell carcinomas and two malignant melanomas [1]. In addition to the cases reported by Cascajo et al, a handful of cases of melanoma arising in seborrheic keratoses have been reported in the literature [2,4-7]. This association is believed to be more than a simple coincidental collision between tumors, and the term compound tumor is proposed as the most appropriate appellation [1,2]. A possible explanation is that neoplasms may derive from the different cells that compose seborrheic keratoses: basal cell carcinoma from the predominant basaloid cells, squamous cell carcinoma from the pale eosinophilic spinous cells and malignant melanoma from the melanocytes admixed among the keratinocytes [1]. Based on previous findings, DeFazio et al postulated that the association of nevus and melanoma with seborrheic keratosis might be due to mutations in growth factors more than just a coincidental collision between tumors [2]. These mutations may result in an altered cell-to-cell communication between melanocytes and keratinocytes that would lead to an abnormal proliferation of melanocytes and/or keratinocytes [2].

Taking into account the potential consequences of overlooking a malignant melanoma, thorough clinical and dermoscopic evaluations should be performed in all patients with seborrheic keratosis in order to provide a correct diagnosis before proceeding to any destructive treatment.