Dermoscopy of a giant desmoplastic melanoma coexistent with rectal adenocarcinoma: a synchronous double primary malignancy

Desmoplastic melanoma (DM) is a very rare subtype with marked differences in both clinical appearance and cytomorphological features [1]. Because DM can mimic a wide variety of lesions, both benign and malignant, it presents a diagnostic challenge to clinicians and pathologists alike [2, 3]. Histopathologically, fibrous stroma occurs in both DM and skin metastases [3, 4]. Even in the case of a giant skin tumour, the possibility of cutaneous solid tumour metastases should always be considered. Skin metastases are found in 0.7–10.4% of all patients with malignant neoplasms of internal organs [5].

An 80-year-old man was admitted to the Skin Cancer and Melanoma Team with a 9-month history of expanding tumour located on the right side of his chest. He also reported rectal bleeding and periodic rectal pain. Physical examination revealed firm, red, partially ulcerated tumour, sized 6 × 7 cm in a parasternal line, relocatable relative to the base surface (Figure 1 A). Dermoscopy of the giant cutaneous tumour revealed the presence of multiple, polymorphous linear and serpentine vessels in unspecific arrangement located on the whitish and reddish structureless background (Figures 1 B, C). Examination of his rectum revealed a polypoid tumour on the anterior wall of the rectum, approximately 2 cm above the anal sphincter. Peripheral lymph nodes in the right axillary fossa were palpable, up to 2 cm in size. Simultaneously, ultrasound of the axillary lymph nodes indicated a reactive lymphadenopathy pattern. We performed a fine-needle aspiration biopsy of clinically palpable lymph nodes in the right axilla. The biopsy showed no evidence of malignant cells. We also conducted an excisional biopsy of the giant cutaneous tumour. We observed, in histopathological examination, desmoplastic melanoma with Breslow’s thickness up to 20 mm, Clark’s level V (Figures 2 A–F). The mitotic rate of the neoplastic cells was increased, up to 14/mm². See the legend to Figures 2 A–F for a detailed description of histopathology with immunohistochemical staining. We measured the surgical excision margins. The deep margin was close, about 1 mm. Moreover, no BRAF mutation was detected. We performed sentinel lymph node lymphoscintigraphy, which revealed a lymph node in the right axillary fossa measuring 2.0 × 1.5 × 1.0 cm. We observed in histopathology 6-mm melanoma metastasis with infiltration of the lymph node capsule. Two months later, we conducted an axillary lymphadenectomy. No additional nodal involvement was found (0/11). The final staging was assessed as pT4bN1b(sn)cM0 (III C) according to the American Joint Committee on Cancer (AJCC) tumour, node, metastasis (AJCC/TNM) 8^th edition classification. The fluorodeoxyglucose positron emission tomography (FDG-PET) scan revealed synchronous rectal cancer. It also excluded the presence of metastases, considering the melanoma diagnosis. An MRI scan revealed a locally infiltrative tumour of the lower rectum which was staged as cT3cN1Mx MRF+ (IIIB). The largest tumour size was 55 mm, with involvement of mesorectal fascia, including the upper edge of the internal sphincter of the anal canal. Colonoscopy and biopsy revealed low-grade rectal adenocarcinoma. The patient was not eligible for adjuvant anti-programmed cell death protein 1 immunotherapy due to planned treatment for rectal cancer. He underwent preoperative radiotherapy (25 Gy/5 days). Two months later, he had an abdominoperineal resection and terminal colostomy. The final pathological staging of adenocarcinoma was ypT2N0 (I). The patient continues to have regular oncological follow-up visits.

Figure 1.

A – Clinical manifestation of desmoplastic melanoma presented as a giant, ulcerated, necrotic tumor located along the parasternal line, measuring 6 × 7 cm and movable relative to the underlying surface. B – Dermoscopy in non-polarized light revealed asymmetry in dermoscopic structure distribution, the presence of multiple polymorphous linear and serpentine vessels in unspecific arrangement located on the whitish and reddish structureless background. C – Dermoscopy in polarized light showed the presence of multiple short white lines located on pinkish – whitish structureless background

Figure 2.

A–F – Histopathological examination revealed desmoplastic melanoma with Breslow’s thickness up to 20 mm, Clark’s level V. Cytological atypia varied from moderate to high, tumor cells presented hyperchromatic, elongated nuclei. Microscopic image showed presence of cellular ulcerated broad infiltration in dermis, with superficial spreading melanoma-like intraepidermal proliferation. The mitotic rate of the neoplastic cells was increased, up to 14/mm2 (haematoxylin– eosin, 15.08× and 10×) (A, B). Perineural invasion was identified without perivascular involvement (haematoxylin– eosin, 17.96×) (C). The immunohistochemical staining was positive for SOX-10 (+++) and S100 (+) and a loss of HMB-45, MelanA and CKPAN expression (SOX-10 6.47× and CKPAN 8.22×) (D, E). Other pathological findings included and a high Ki-67 proliferation index of up to 50% (17.77×) (F). Surgical excision margins were measured, the deep margin was close, about 1 mm. The staging was pT4bN1b(sn)cM0 (III C) according to the American Joint Committee on Cancer (AJCC) tumor, node, metastasis (AJCC/TNM) 8th edition classification

Skin metastases can present as solitary, palpable, firm or flexible reddish nodules, lacking specific clinical diagnostic criteria [5]. In evaluating the effectiveness of dermoscopy for metastatic skin tumours, there is still a lack of comprehensive data. Polymorphous vascular structures frequently observed in metastatic nodules are associated with neovascularization found in histopathological examination [6]. The most commonly observed type of vessels is linear serpentine vessels, present in 56.3% of all cutaneous metastases of different primary malignancy, including those originating from gastrointestinal cancer [6, 7]. Other dermoscopic patterns of non-pigmented cutaneous metastases consist of dotted vessels, ulceration, background erythema and structureless white pattern which correlates with fibrosis [6, 7]. The same dermoscopic features may occur in DM, making it difficult to diagnose due to its rare occurrence. In the histopathological examination, the desmoplastic component is defined by melanocytes located between the connective tissue elements [1, 8]. DM accounts for approximately 1% to 4% of primary cutaneous melanomas [9]. Previous studies have shown that risk factors for DM include excessive sun exposure, with the head and neck being the most common sites in both sexes. The median age of patients is 60–70 years (compared to non-DM patients with a median age of 50 years) [9]. There is also a male predilection, with a male to female ratio of 2 : 1 [9–11]. DM does not fulfil the classic ABCDE criteria for melanoma. Like other amelanotic melanomas, it can be clinically confused with both benign and malignant skin lesions. These include intradermal nevus, pyogenic granuloma, dermatofibroma, neurofibroma, piloleiomyoma or basal cell carcinoma, squamous cell carcinoma (both in situ and invasive) and Merkel cell carcinoma [10, 12, 13]. The main dermoscopic criteria of DM are chrysalis, milky red or homogeneous hyperpigmented areas, atypical network, polymorphous vascular pattern, regression pattern with white scar-like areas and multiple colours. Typical melanocytic patterns, such as nodules or a pigmented network, are observed in 43–60% of DMs [9, 14]. Melanoma survivors have an almost 9 times higher chance of developing a subsequent melanoma and a significantly higher risk of other cancers such as breast, prostate, thyroid, colorectal and non-Hodgkin’s lymphoma [15]. The timing of a synchronous primary malignancy may affect prognosis.

Among gastrointestinal cancers, colorectal cancer often spreads to the skin. Both DM and skin metastases may present as a pink nodule with a polymorphic vascular pattern, together with a regression pattern including white scar-like areas observed in dermoscopy. The presented case illustrates that diagnosing and managing synchronous dual primary malignancies, particularly in an elderly patient, is challenging.

Funding Statement

Funding Not applicable.

Ethical approval

Approval number: KB/430-29/19.

Conflict of interest

The authors declare no conflict of interest.