Desmoplastic Melanoma of the Chest Wall: a Diagnostic Dilemma

Abstract

Desmoplastic melanoma is an extremely rare subtype of malignant melanoma comprising only 1% of all the cutaneous melanomas. Being amelanotic and owing to its histopathological features of spindle cells lying in a collagenized stroma, it is often misdiagnosed as a dermatofibroma or scar tissue. The present case study describes a case of desmoplastic melanoma of the chest wall where the final diagnosis could be arrived at only after an extensive immunohistochemical panel to exclude other spindle cell proliferations.

Introduction

Desmoplastic melanoma (DM) is an extremely uncommon subtype of malignant melanoma comprising only 1% of all the primary cutaneous melanomas with a global incidence of 2 cases out of 1 million inhabitants [1, 2]. Conley et al.[3] described this entity for the first time in 1971 as a variant of spindle cell melanoma. It has a predilection towards the head and neck region with a male preponderance as male-to-female ratio is 2:1. It always poses a diagnostic challenge to clinicians because of its amelanotic plaque, papule, or nodular presentation [4]. It tends to be misdiagnosed as scar, dermatofibromas, or benign nevus as there is spindle cell proliferation in a collagenized stroma leading to a potential diagnostic pitfall [1]. Here, we present a challenging case of desmoplastic melanoma of the chest wall in a 49-year-old male diagnosed on histopathology and extensive immunohistochemical panel to rule out other spindle cell neoplasms.

Case Report

A 49-year-old man presented in the surgical outpatient department with a 1-year history of a 3-cm nonpigmented, nodular mass on the anterior chest wall. It was painless and had increased in size over a period of 4 months. No other cutaneous lesion was identified, and his family history was uneventful. The mass was poorly circumscribed and non-tender. The overlying skin was slightly erythematous; however, no ulceration or pigmentation was noted. A computed tomography (CT) was performed which showed a 3 × 2.5 × 1.8 cm homogenous enhancing soft tissue density mass in the subcutaneous plane of the left anterior chest wall (Fig. 1a). A core needle biopsy was also attempted; however, on microscopy, few pleomorphic spindle cells were seen in a fibro-collagenous stroma, and immunohistochemistry was inconclusive due to the scanty nature of the tissue. The lesion was resected with adequate surgical margins and sent for histopathological examination. Grossly, a skin-covered soft tissue mass was received which on cut showed a gray-white growth over the skin measuring 2.5 × 2 × 1.6 cm, and all the surgical margins were uninvolved (Fig. 1b, c). Hematoxylin- and eosin-stained sections showed an invasive tumor (Clark level 4) in the superficial and deep dermis having a connection with the epidermis at places. The tumor cells were present singly scattered and in small clusters occasionally. The tumor cells were moderately pleomorphic, having spindle to ovoid-shaped morphology and oval to elongated hyperchromatic nuclei with eosinophilic cytoplasm. These cells were embedded in a desmoplastic collagenous and myxoid stroma exhibiting neurotropism. At places, lymphoid aggregates were also present, and many atypical mitotic figures could be identified. Based on the morphology, an initial panel of immunohistochemistry (IHC) was done to confirm the lineage of the tumor cells which included S100, SMA, desmin, vimentin, EMA, pan-CK, and HMB-45. Among them, only S100 was diffusely positive which ruled out any epithelial and muscle origin. Owing to the superficial location of the tumor and its connection with the epidermis, a diagnosis of malignant peripheral nerve sheath tumor or neurofibroma was less likely. Another panel of IHC was performed to rule out the above diagnosis which included Melan-A, SOX 10, p53, and Ki67. The tumor cells were positive for SOX10 and p53; also, the cells were highlighted by SOX10 in the region of epidermal connectivity. The Ki67 proliferation index was approximately 35–40% (Fig. 2). Based on the morphological features and immunohistochemical expression, a definite diagnosis of desmoplastic melanoma was made. As perineural invasion was also identified, adjuvant radiotherapy was also given, and the patient was kept under careful follow-up.

Fig. 1.

Radiological and gross findings. a Computed tomography showed a homogenous enhancing soft tissue density mass in the subcutaneous plane of the left anterior chest wall. b–c Gross examination exhibited a skin-covered soft tissue mass which on cut surface showed a homogeneous gray-white growth over the skin measuring 2.5 × 2 × 1.6 cm

Fig. 2.

Histopathological and immunohistochemical findings. a Sections examined demonstrated an invasive tumor (Clark level 4) in the superficial and deep dermis having a connection with the epidermis at places (inset exhibiting lymphoid aggregates) (hematoxylin and eosin, × 40). b–c High power exhibited moderately pleomorphic tumor cells, having spindle to ovoid-shaped morphology and oval to elongated hyperchromatic nuclei with eosinophilic cytoplasm embedded in a desmoplastic collagenous and myxoid stroma (hematoxylin and eosin, × 400). d–f Immunohistochemistry showed that the tumor cells were positive for SOX-10 (d) and S100 (e) while being negative for Melan-A (f) (× 400)

Discussion

DM is a rare variant of malignant melanoma which creates a diagnostic dilemma for clinicians and pathologists in the realm of melanocytic tumors. It occurs in sun-exposed regions and most commonly in the head and neck and frequently affects men. The present case was also a male patient; however, the lesion was at an uncommon site when compared to previously reported cases [5, 6]. In the previous reports of Godoy et al.[7] and Treacy et al.[8], the site was lower lip, and literature mentions lower lip is a far more common site in males [9].

There are different theories regarding the mechanism of desmoplasia in DM. One of the theories suggests that the tumor cells induce a host response in the form of a desmoplastic reaction comprising collagen and fibroblastic proliferation [10]. The other hypothesis explains that tumor cells produce collagen and fibroblasts as they have acquired the functional capacity of fibroblasts [3].

DM is classified as pure and mixed depending on the percentage of the desmoplasia. A > 90% of desmoplasia is pure form, and if conventional melanoma is > 10%, then it is classified as mixed one. The present case was a pure form of DM [11]. When compared to non-desmoplastic melanoma, lymphatic metastasis is rarely seen in DM (0–18.8%); however, the tumor itself infiltrates and is locally aggressive, and to show neurotropism, a higher Clark level (4 and 5) is required which was present in this case also [12].

The histopathological findings include nonpigmented spindle cell proliferation, with abundant collagenous stroma and foci of myxoid matrix with cells showing moderate to marked atypia. One important histological clue is lymphoid aggregates, and tumor tends to be deep showing neurotropism [13]. For definitive diagnosis in almost all cases, IHC is required as they tend to be amelanotic, and other spindle cell lesions need to be ruled out as was in this also. The conventional melanoma markers including Melan-A and HMB45 are usually negative or only weakly positive in 20% of the cases, whereas S100 and SOX10 seem to be positive in 96% and 93% of the cases [11]. However, these two markers are also showing positivity in many other spindle cell neoplasms including neurofibroma (NF). Key histological features to differentiate it from NF are poor circumscription, arising from epithelium, fibroplasia, degree of atypia, and lymphoid aggregates. p53 staining is somewhat also helpful in differentiating the two entities [14].

The first line of management includes a wide local excision to minimize chances of recurrence. The role of sentinel lymph node biopsy is unclear due to the low risk of nodal involvement. Adjuvant radiotherapy is not routinely advised, but in recurrent cases or patients associated with a risk of distant metastasis, it is recommended. A decrease in the rate of local recurrence has been observed recently in cases who received adjuvant radiotherapy [8, 15].

To conclude, desmoplastic melanoma is an unusual variant of malignant melanoma commonly occurring in the head and neck region but can also occur in other rare locations including the chest wall. It is a locally aggressive tumor with a tendency to recur, so a negative margin is a must. We have highlighted the immunohistological features and important clues for the diagnosis of this rare entity.

Author Contribution

AAZ, writing original draft and visualization. SZ and SA, writing—review and editing, conceptualization, and visualization. PG, writing original draft. This paper has been prepared by the abovementioned authors and reviewed and agreed upon for submission. The requirements for authorship as stated above in this document have been met, and that each author believes that the manuscript represents honest work.

Declarations

Ethics Approval

Not applicable, because this article does not contain any studies with human or animal subjects.

Consent for Participation

Informed patient consent was taken before publication of the article. Any identifying details (such as name, date of birth) of the patient will not be published.

Consent for Publication

Informed consent was sought from patient regarding participation and publication.

Conflict of Interest

The authors declare no competing interests.

Previous Presentation/Publication

None.