A rare case of acral amelanotic melanoma, nodular type

Abstract

Amelanotic melanoma is a rare melanoma subtype, and it is even more rare when it occurs at an acral site. We here present a case of a nodular amelanotic acral melanoma (NAAM) occurring on the heel of an 83‐year old female. It presented as an ulcerated pink nodular growth on the heel, which clinically mimicked other nodular non‐pigmented lesions, causing a delay in diagnosis until it was biopsied. This case is a demonstration of the critical importance to include NAAM in the differential diagnosis of nodular non‐pigmented skin lesions as to avoid delay in diagnosis and disease progression, in which early detection can provide the most modifiable prognostic factor.

1. INTRODUCTION

Acral acral amelanotic malignant melanoma (aMM) is rare type of melanoma and it is easily overlooked, leading to a delayed diagnosis. Acral aMM usually presents as an erythematous nodule or plaque and is often clinically misdiagnosed as a benign lesion initially.1, 2, 3 Unfortunately, because of delayed diagnosis, this malignancy is usually diagnosed at an advanced stage with nodal metastasis and is associated with a poor prognosis.4, 5, 6

2. CASE REPORT

An 83‐year‐old Hispanic female presented with a growing non‐healing lesion on her left heel. Her medical history includes hypertension, hyperlipidemia, and obesity. She has also been wheel chair bound for the prior 2 years. She complained that she had a growing “lump” on her heel and had become painful and ulcerated. She was seen by a podiatrist and by a wound care specialist who had prescribed treatments of Alginate, dry dressings, and an offloading shoe. However, the foot lesion continued to worsen and enlarge over time. The clinical differential diagnosis at the time of biopsy included neoplasm, such as verrucous carcinoma and infection. A skin biopsy was finally performed and revealed an invasive melanoma. At surgery, the patient had a 4 cm × 4 cm tan‐pink exophytic, fleshy nodule on her left heel (Figure 1). The tumour was excised with a 2‐cm margin.

Figure 1.

Surgically excised specimen of a large flesh coloured exophytic and ulcerated nodule removed from the left heel

The received surgical skin specimen consisted of a 9.0 × 6.0 × 1.0 cm³ ellipse of skin and fat with a central overlying 5.0 × 4.2 × 0.8 cm³ tan‐pink raised exophytic ulcerated nodule. Sectioning through the exophytic neoplasm revealed a tumour depth of 1.0 cm.

Microscopically, the tumour demonstrated an invasive amelanotic melanoma, nodular type, with a Breslow thickness of 10 mm, Clark level V. It grew into the fat with a diffuse vertical growth pattern composed of solid sheets of atypical polygonal cells occupying the entire dermis. Epidermal involvement was not seen in this ulcerated specimen. The infiltrating neoplastic cells displayed hyperchromatic nuclei, prominent nucleoli, and scanty cytoplasm. The immunostaining Melan A highlighted rare scattered cells with weak uptake in this amelanotic melanoma. Mitotic figures were conspicuous with a mitotic rate 9/mm². The one sentinel lymph node was identified and was negative for metastatic tumour. This acral amelanotic melanoma, nodular type, was staged as pT4b pN0(sn) (Figures 2, 3, 4, 5).

Figure 2.

A, H & E stain shows abrupt transition from normal squamous epithelium to exophytic lesion composed of vertical growth of sheets of polygonal cells (20×). B, H & E stain shows invasive nodular pattern of growth (20×). C, H & E stain shows tumour cells with hyperchromatic nuclei, prominent nucleoli in some of the cells, and scant cytoplasm (40×)

Figure 3.

Immunostaining with HMB45 and Melan A highlight positive tumour cells (40×)

Figure 4.

S100 and HITF immunostaining, respectively, both are positive in tumour cells and highlight invasion into the adipose tissue (20×)

Figure 5.

Positive immunohistochemical staining with S100, Melan A, and HMB45. They highlight tumour cells invading into surrounding adipose tissue (40×)

3. DISCUSSION

Amelanotic malignant melanoma (AMM) is a relatively rare subtype with the incidence of 1.8 of all malignant melanoma cases.4, 7 When the AMM occurs on the lower extremity, it may be misdiagnosed as other non‐pigmented skin lesions, including diabetic foot ulcer, infection, pyoderma gangrenosum, basal cell carcinoma, squamous cell carcinoma, and other neoplasm.8, 9 The nodular melanoma is the second most common type of melanoma and is characterised by an aggressive vertical growth pattern into the dermis.⁹ It often arises in legs and it accounts for about 15% of all diagnosed melanomas.8, 10 However, only about 5% of nodular melanoma are non‐pigmented.11, 12 As of 2016, warner et al reported the first case of nodular malignant melanoma of the heel in a non‐fair skinned individual in the past 40 years. Compared with the nodular melanoma, acral lentiginous melanoma accounts for about 4%‐10% of all melanoma diagnoses.8, 13, 14 However, acral lentiginous melanoma is pigmented and is more common in people with dark skin, such as Asian, African, and middle easterners.13, 15 Lentiginous melanoma is characterised by a radial growth pattern depicted by lateral neoplastic spread with localization to the epidermis.16

A delayed diagnosis of a malignancy occurring at a non‐healing wound site17, 18 can result in advanced disease with an increased morbidity and mortality, as well as increased health‐care cost. Biopsy of a non‐healing foot ulcer is extremely important for proper early diagnosis and treatment.

To address the diagnostic challenges associated with chronic non‐healing foot lesions, Bristow et al19 have created the acronym “CUBED” for the criteria identifying the lesions of concern (Table 1). According to the “CUBED” criteria, when any two features apply, the patient should be referred to dermatologist. To exclude malignancy, skin biopsies should be taken without delay in patients who have recalcitrant ulcers. This case reinforces the need to re‐evaluate and to biopsy when confronted with a chronic non‐healing ulcer.

Table 1.

CUBED criteria for acral lesions that need referral to dermatologist. Adapted from Bristow et al¹²

Bristow “CUBED” criteria   C = Coloured variation in a lesion U = Uncertain diagnosis B = Bleeding lesions on the foot or under the nail E = Enlargement of deterioration of a lesion or ulcer despite therapy D = Delay in healing of any lesion beyond 2 months

4. CONCLUSIONS

Although the acral amelanotic melanoma is uncommon, it can be overlooked and can masquerade as other non‐pigmented lesions, which can lead to a delayed diagnosis. This case underscores the importance that the amelanotic melanoma should be included in the clinical differential diagnosis of non‐healing, non‐pigmented skin lesions.

Mohammed Saeed D, Braniecki M, Groth JV. A rare case of acral amelanotic melanoma, nodular type. Int Wound J. 2019;16:1445–1449. 10.1111/iwj.13212