Survival Outcomes and Treatment Strategies in Primary Thyroid Lymphoma: A Population-Based Study of 401 Cases from the Tokyo Cancer Registry

<b><i>Background:</i></b> There is limited information about the clinical behavior and no standardized treatment guidelines for primary thyroid lymphoma (PTL). Prognostic factors and treatment outcomes remain poorly defined despite diagnostic and therapeutic advancements. We evaluated PTL survival outcomes and treatment strategies, using a large population-based cohort from the Tokyo Cancer Registry (TCR), a government-operated database that systematically collects cancer incidence and outcome data in Tokyo, Japan. <b><i>Patients and Methods:</i></b> This retrospective, population-based study analyzed PTL cases registered in 2012-2020 in the TCR. The patients (<i>n</i> = 401) were identified through an International Classification of Diseases for Oncology, third edition topography code C73.9 (thyroid gland) and nonthyroidal lymphoma ICD-10 codes. <b><i>Results:</i></b> The median follow-up was 3.3 years (interquartile range, 1.2-5.5 years). Disease-specific mortality was concentrated in the first two years postdiagnosis, particularly in the initial six months. Advanced age (≥80 years) and diffuse large B-cell lymphoma (DLBCL) were associated with poorer overall survival (OS) and disease-specific survival (DSS). The current lymphoma staging systems do not significantly differentiate survival outcomes. Favorable outcomes were observed with localized treatments, including curative surgery alone, for stage IE PTL. <b><i>Conclusions:</i></b> Disease-specific mortality was highest in the first two years, particularly the first six months, highlighting this as a critical management period and the importance of timely treatment. Despite recent treatment advances that have improved the overall prognosis and reduced prognostic differences among disease stages, age at diagnosis and histological subtype remain key OS and DSS determinants, with older patients and DLBCL patients experiencing poorer outcomes. Notably, favorable outcomes were observed in selected Stage IE cases treated with surgery alone, suggesting that less-intensive treatment may be appropriate for certain PTL patients.