Second primary mediastinal grey-zone lymphoma following treatment for classical Hodgkin lymphoma: a rare case report.

BACKGROUND: Gray-zone lymphoma (GZL) is a rare and biologically distinctive B-cell lymphoma that exhibits overlapping clinical and pathological features between classical Hodgkin lymphoma (cHL) and mediastinal large B-cell lymphoma (PMBL). Mediastinal Gray-zone lymphoma (MGZL) occurring as a second primary malignancy following treatment for cHL is exceedingly rare, and both its pathogenesis and optimal clinical management remain poorly characterized. CASE PRESENTATION: A 22-year-old woman diagnosed with cHL in 2020 achieved complete remission after ABVD chemotherapy. Five years later, a new mediastinal mass was identified during routine follow-up. Excisional biopsy via video-assisted thoracoscopic surgery (VATS), together with comprehensive immunohistochemical and molecular analyses, confirmed a diagnosis of secondary MGZL. The patient subsequently underwent salvage chemotherapy followed by autologous stem-cell transplantation, achieving clinical remission. CONCLUSION: In long-term survivors of cHL, the emergence of a new mediastinal mass necessitates repeat biopsy and precise pathological reassessment rather than presumption of relapse. Second primary lymphomas, such as MGZL, require individualized treatment strategies.