Cutaneous neoplasms from different cell types can exist within the same lesion. These can be classified into four subtypes which are collision tumour, combined tumour, colonization and biphenotypic tumour. The presence of a melanoma component in these tumours is very rare. Herein we present a singular case of two synchronous dineoplastic cutaneous tumours: a squamomelanocytic tumour and a collision consisting of melanoma and seborrheic keratosis. Additionally, we performed a literature review of all squamomelanocytic tumours published until date, including our case.
Keywords: Biphenotypia, collision tumour, combined tumour, melanoma, squamomelanocytic tumour
Cutaneous neoplasms from different cell types can exist within the same lesion. These can be classified into four subtypes which are collision tumour, combined tumour, colonization and biphenotypic tumour.[1] Combined tumours are those where the two components are intimately intermingled. The presence of a melanoma component is very rare and can be found in different subtypes. The most frequent subtypes are, in order of frequency: squamomelanocytic tumour (SMT), basomelanocytic and the trichoblastomelanoma.[2] Collision tumours are those with obvious distinction of the two components. The most common subtype is melanocytic nevus with basal cell carcinoma, whereas collisions with a melanoma component are exceptional.[3],[4]
Herein we present a singular case of an elderly man that concurrently presented with two dineoplastic cutaneous tumours: a squamomelanocytic tumour and a collision tumour of melanoma with seborrheic keratosis. Furthermore, we reviewed the clinical and histopathological characteristics of all SMT published until date.
Case ReportA 84-year-old male patient with history of cardiovascular disease, colorectal cancer with metastatic disease and multiple non-melanoma skin cancers presented with a four-month history of an ulcerated lesion in the left mandibular angle. On physical examination, he presented a one-centimetre black ulcerated tumour [Figure 1]a. On dermoscopic examination, homogeneous brown-pigmented structureless areas, polymorphous vessels and milky-red areas were observed. At the same time, a two-centimetre asymmetric macule with poorly defined borders and heterochrome pigmentation in the forehead was found [Figure 2]a. On dermoscopic examination, a brownish pseudonetwork with asymmetric pigmented follicular openings, dark rhomboidal structures and dark-brown-coloured homogeneous areas were observed.
Figure 1: Squamomelanocytic tumour. (a) Clinical image of a black ulcerated tumour in the mandibular angle. (b) Low-power magnification showing nests of atypical melanocytes with admixed squamous cell carcinoma (x4.6). (c) High-power magnification depicting the intermingling of pleomorphic keratinocytes and atypical melanocytes (x10.2). (d) Immunohistochemical staining with MELAN-A showing melanocytic component (x9.6). (e) Immunohistochemical staining with cytokeratin AE1/AE3 showing squamous component (x7.9)Figure 2: Collision of melanoma in-situ with seborrheic keratosis. (a) Clinical image of an asymmetric macule with irregular, poorly defined borders and heterochrome pigmentation in the forehead. (b) Low-power magnification showing a collision of a melanoma in-situ, lentigo maligna type, with a seborrheic keratosis (black arrows) (x 7.7). (c) High magnification of melanoma in-situ component, with nests of atypical melanocytes along dermal–epidermal junction (x33.4). (d) Immunohistochemical staining with MELAN-A showing melanocytic component (x15.8)In suspicion of malignancy, an excisional biopsy of the left mandibular lesion was performed. Microscopic examination showed an extensively ulcerated exophytic tumour with focally pigmented expansive nodules infiltrating the reticular dermis. On high-power examination, the tumour consisted of sheets and irregular nests of atypical squamous cells intermingled with large atypical pigmented dendritic cells. In the immunohistochemical study, melanocytic cells showed positivity for Melan-A, HMB-45 and SOX-10 and squamous and basaloid cells expressed positivity for cytokeratin AE1/AE3, cytokeratin 5/6 and epithelial membrane antigen [Figure 1]b, [Figure 1]c, [Figure 1]d, [Figure 1]e. A diagnosis of SMT was rendered. The Breslow depth of the tumour was 3.8 mm.
On the other hand, the histopathological exam of the forehead lesion was compatible with a collision tumour of melanoma in-situ, lentigo maligna type, with seborrheic keratosis [Figure 2]b, [Figure 2]c, [Figure 2]d.
Laboratory investigations and initial staging consisting on full body scan did not show any alterations. Clinical follow-up was decided given patient's comorbidities. One year after surgery, patient died due to its metastatic colorectal cancer without recurrence or progression of its cutaneous neoplasms.
DiscussionSMT is the most frequent type of combined cutaneous tumour with a melanoma component. The term of SMT was first coined by Rosen et al. in 1984 to describe a neoplasm composed of a squamous cell carcinoma admixed with a melanoma.[5] Due to the different terms that have been used to name these tumours, such as combined, colliding, biphasic, contiguous or colonizing tumours, it is difficult to determine how many cases have been reported.
Based on our literature review, 37 cases of SMT have been described, including our patient [Table 1].[6],[7],[8],[9],[10] Our results showed an average patient age of 68.5 years (range: 32–94 years). The tumours were more common in males (66.7%), frequently involving the head and neck region (66.7%). The vast majority of melanoma components were invasive (83.3%), with a mean Breslow of 2.73 mm; nevertheless, only 2 out of 13 patients registered micrometastasis on sentinel node biopsy at diagnose. Mean follow-up was 29.8 months (range 3–167 months) [Table 2].
Table 2: Clinical and histological characteristics of squamomelanocytic tumoursCollision tumours can be composed of two benign tumours, a benign and malignant tumour, and two malignant tumours. The most frequently described subtype is a collision of a melanocytic nevus and basal cell carcinoma. Collision of melanoma with seborrheic keratosis is extremely rare.[3],[11]
The histogenesis of multiple skin neoplasms at one site remains uncertain. Several theories have been postulated such as melanocytic colonization, squamous pseudoepitheliomatous hyperplasia, tumour–tumour metastases, tumour collision, true biphenotypia theory and field cancerization theory. There is no high-level evidence to support only one of them. Field cancerization theory proposes that exposure to a common carcinogenic factor, such as ultraviolet radiation, within a field area facilitates proliferation of neoplastic cells and the development of two different tumours within one lesion.[8],[12] In the present case, field cancerization theory might be the most plausible hypothesis due to patient's history of chronic sun exposure and non-melanoma skin cancer.
The biologic behaviour and clinical prognosis of these entities are difficult to assess because of its rarity and the low evidence available. There are multiple reports that suggest that the melanomas seen in these tumours have a better prognosis than those seen alone. Local recurrences and metastasis are rare.[12],[13],[14],[15],[16],[17]
ConclusionsIn conclusion, SMT is a rare entity defined by the presence of two components that are intimately intermingled. Its histogenesis remains unclear, and it has to be differentiated from collision tumour. Although it is recommended to be treated as a melanoma, it might have better prognosis than common melanoma. Besides, collision tumours can represent a diagnostic challenge. It is mandatory to perform a complete clinical and histopathological exam in order to make an early diagnosis and treatment. Further studies assessing for the biologic behaviour and prognosis of combined and collision tumours with a melanoma component are needed to determine the correct management and follow-up.
Acknowledgement
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