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A 64-year-old man has had an eczematous rash in the groin, buttocks and lower abdomen for 4 years. He has been treated with multiple courses of topical corticosteroids, two courses of oral antifungals (on a presumptive diagnosis of tinea), and 3 months of narrowband UVB phototherapy. The rash has persisted, with new patches appearing on the trunk. Examination shows ill-defined, red-brown, atrophic, scaly patches in a bathing-trunk distribution, with one infiltrated plaque on the left lower back. There is no lymphadenopathy or hepatosplenomegaly. A 4 mm punch biopsy shows a band-like dermal infiltrate of atypical lymphocytes with epidermotropism and a single Pautrier microabscess. PCR for the T-cell receptor (TCR) gamma chain shows a single dominant peak. CD4+ T cells show aberrant loss of CD7. The full blood count, peripheral blood flow cytometry, serum LDH and whole-body PET/CT are normal. TCR gene rearrangement on peripheral blood is negative.
Questions
a) What is the most likely diagnosis, and which clinical, histological, immunophenotypic and molecular features support it? (3 marks)
b) What is the TNMB stage, and what additional baseline investigations are appropriate before starting treatment? (2 marks)
c) Outline your first-line management plan, including the skin-directed and systemic options and the trigger to escalate. (3 marks)
d) List four red flags that should prompt escalation to a haemato-oncology multidisciplinary team. (2 marks)