Desmoplastic melanoma of the nail

The utility of SOX10 in mixed type desmoplastic melanoma with lymph node metastasis of the spindle cell component: A cautionary tale of inattentional blindness

Desmoplastic melanoma (DM), a type of spindle cell melanoma separated into pure desmoplastic melanoma (PDM) and mixed desmoplastic melanoma (MDM) subtypes, can be a diagnostic challenge and easily confused for dermal scar, especially PDM. We report a 65-year-old white man who received a left thumb amputation after an initial biopsy for melanoma, an unclassified type with epithelioid morphology. The amputation and sentinel lymph node specimens were significant for residual melanoma with epithelioid morphology, dermal scar, and a slightly expanded "scar-like" capsular area in one of seven lymph nodes, which was diffusely positive for SOX10 on reflex sentinel lymph node immunohistochemical protocol. On re-review of the amputation "scar" like area, a subsequent SOX10 stain confirmed the diagnosis of MDM in this area with epithelioid and spindle cell morphology, significantly upgrading the tumor stage. We share this case to highlight: (i) MDM, although exceptionally uncommon, can result in a pure spindle cell lymph node metastasis, (ii) to encourage increased utilization of SOX10 to assess sentinel lymph node biopsies, especially in the context of melanomas with a spindle cell component, and (iii) share an example of inattentional blindness which was fortunately identified by reflex sentinel lymph node immunohistochemical protocols.

Desmoplastic melanoma arising in the ankle

Desmoplastic melanoma (DM) is an uncommon but potentially devastating malignancy that can be cured with early recognition and surgery. DM often occurs in elderly men and develops on sun-exposed areas with the head and neck being the most common site of origin followed by the extremities and trunk. We report a rare case of DM occurring in the ankle in an 85-year-old woman. Magnetic resonance imaging of the affected ankle showed a 4.3 x 4.3 x 2.5 cm sized mass which was located in the subcutaneous region, attached to lower leg muscles, the fibula, and the calcaneus. No metastasis to the lung, liver, bones or abdominal lymph nodes was found. In spite of below knee amputation, the patient died of lung metastases 10 months after surgery. Among several factors causing early death of the patient, a large size, a deep location and rapid growth of the tumor seem to be most important.