LY16 Primary cutaneous follicle centre lymphoma arising at a COVID-19 vaccination site with spontaneous regression

Abstract

Primary cutaneous follicle centre lymphoma (PCFCL) is an indolent cutaneous B-cell lymphoma that may rarely show spontaneous regression. The impact of immune stimulation, including vaccination, on the behaviour and morphology of cutaneous lymphomas remains poorly understood. We present a case of a 73-year-old man who presented with an > 30-year history of an asymptomatic truncal eruption consisting of erythematous patches and indurated plaques. He developed an erythematous raised lesion over the right deltoid directly following COVID-19 vaccination to this area, which progressively enlarged into two tumoral nodules measuring 5–6 cm. Skin biopsies from the right arm and trunk demonstrated a diffuse dermal B-cell infiltrate (CD20+, PAX5+) coexpressing CD10 and BCL6, with variable BCL2 positivity and a high proliferative index (Ki-67 ∼80%). Molecular genetic analysis confirmed a monoclonal B-cell population with concordant immunoglobulin gene rearrangements across multiple biopsy sites, supporting a diagnosis of the diffuse variant of PCFCL. Full staging with positron emission tomography–­computed tomography demonstrated fluorodeoxyglucose avidity confined to the right deltoid lesions, with no systemic disease and a clear bone marrow. Notably, the deltoid tumours involuted spontaneously prior to any treatment, while the indurated truncal lesions progressed. Repeat biopsies demonstrated persistent clonal B-cell infiltrates, with admixed CD4-predominant T cells raising clinicopathological concern for mycosis fungoides. However, T-cell clonality was not diagnostic. The patient received rituximab monotherapy with near-complete clearance. This case is notable for tumoral PCFCL with high-grade appearance arising at a COVID-19 vaccination site with spontaneous regression, supporting a potential antigen-driven immunological trigger. Vaccine-associated triggering or apparent transformation of PCFCL represents an unanswered aspect of dermatological oncology and may influence future diagnostic and management approaches.