Estimation of Relapsed/Refractory Follicular Lymphoma Patients on Therapy in the United States

Background: Follicular lymphoma (FL) represents approximately 20-25% of non-Hodgkin lymphomas (NHL). In contrast to patients with more aggressive NHL, patients with FL have a heterogenous course of disease in which some can spend extended periods in an initial watch-and-wait state and/or within a single line of treatment. As such, these patients may have multiple relapses and a variety of clinical features that may impact disease course (eg, double-refractory disease, increased Follicular Lymphoma International Prognostic Index (FLIPI) scores, high Ann Arbor disease stage, older age, etc.). The objective of this study was to estimate the number of treated patients with FL in each line of therapy (LOT) to better understand the proportion with relapsed or refractory (R/R) disease in the US while accounting for distributions of LOTs within a baseline prevalent population and annual trends in treatment initiation by LOT.

Methods: Two companion models were developed from a US perspective: 1) an epidemiologic model that utilized FL incidence and survival data from the Surveillance, Epidemiology, and End Results (SEER) program to project the size of the prevalent population; and 2) a state-transition model describing the proportion of patients with FL initiating treatment and time on treatment by line of therapy. Within the state-transition model, hypothetical incident cohorts were simulated annually to follow FL treatment patterns and survival trajectories until a “steady-state” was reached regarding the distribution of LOTs in the prevalent population. Model inputs were based on data from published literature. Several published sources were identified regarding estimates of treatment rates by line of therapy, with base-case values based on physician survey: 51% for first LOT, 32% for second LOT, and 31% for third and successive LOTs. This distribution was then applied to a baseline prevalent population and subsequent incident cohorts were modeled annually over a 3-year time horizon.

Results: In 2022, the estimated FL prevalent population in the US was 154,922. Over a subsequent 3-year period combining the prevalent patients with newly incident patients, the model projected 10,399 patients initiating first-line treatment, 3197 initiating second-line treatment, and 975 initiating third-line treatment.

Conclusions: While incidence of FL initial diagnosis in the US is well reported, there are limited data describing prevalence or population makeup with respect to LOT. While many patients can benefit from long remissions after first-line therapy, a portion of patients experience R/R disease and require further treatment. Estimation of the R/R FL population can support with planning of treatment needs as novel therapies emerge in the US.