CPC10 A curious case of recurrent melanomas and field change confined to the left thigh over 25 years

Abstract A 52-year-old woman presented in 1999 with an atypical erythematous plaque on her left thigh containing a flesh-coloured nodule surrounded by four pink scaly papules. She had no significant past medical, drug or family history. Excision of the nodule revealed an amelanotic malignant melanoma (MM) of Breslow thickness (BT) 1 mm. Biopsies of the four surrounding lesions confirmed satellite MM in one, with no radiological evidence of metastases. She received adjuvant interferon therapy for 1 year. Repeat imaging was normal. Eighteen years later, she developed a new pigmented lesion on her left thigh confirmed as MM (0.9 mm BT), with three further erythematous plaques on the left thigh reported as (i) proximal left-thigh MM (1.08 mm BT), (ii) middle-left-thigh amelanotic MM (0.6 mm BT) and (iii) left-thigh MM (1.7 mm BT). Wide local excision (WLE) failed to obtain histological clearance of (i) and (iii), with mildly dysplastic naevus and melanoma in situ (MiS), respectively, at the peripheral margins. Reflective confocal microscopy (RCM) was used to guide further surgery, with continued incompletely excised MiS and field change at the margins. Eighteen months later she presented with another MiS and MM (0.5 mm BT) on the left thigh. Imiquimod 5% once daily for 8 weeks to the affected area was instigated to treat any residual in situ component. BRAF, CDKN2A, CDK4 and BAP1 showed no pathological variants, and xeroderma pigmentosum testing was negative. Six months later a further MM (1.2 mm BT) on the left thigh was treated with WLE and skin graft. Sentinel lymph node biopsy was deemed not possible due to previous multiple surgical excisions. Ultrasound groin scan and whole-body FDG-PET computed tomography showed no occult metastases. Several months later, another MM (0.5 mm BT) was excised at the edge of the graft site. Residual dysplastic lentiginous proliferation at the edge with no MM was reported on the 1-cm WLE. This represents a complex case with recurrent MM, often indistinguishable from primary MM histologically. Widespread dysplastic field change evidenced by involvement at the edges of the WLEs and the RCM images was also challenging. RCM can be a noninvasive adjunct in identification of superficial skin tumours. Adjuvant interferon therapy for high-risk MM has demonstrated an increase in disease-free survival (Petrella T, Verma S, Spithoff K et al. Adjuvant interferon therapy for patients at high risk for recurrent melanoma: an updated systemic review and practice guideline. Clin Oncol 2012; 24: 413–23). This may have contributed to the 18-year delay between her first and second melanomas, as well as her complex, recurrent presentations and ongoing local confinement of the MM to the left thigh with lack of disease progression.