LTB-TREAT: A validated international prognostic model for time to treatment in low tumour burden follicular lymphoma.

Watchful waiting (WW) in low tumour burden follicular lymphoma (LTB FL) defers treatment. There is a need to develop a model to predict time to treatment (TTT). We aimed to develop and externally validate a model for TTT in LTB FL. We conducted a retrospective analysis across eight centres within the Australasian Lymphoma Alliance. Two hundred and twenty-nine patients were included between 2004 and 2022 with a median follow-up of 5.0 years (range 0.5-17.8 years) and a median age was 64 years. All patients were Group d'Etude des Lymphomes Folliculaires (GELF) negative and managed with WW. Elevated lactate dehydrogenase and >4 nodal areas were independent prognostic factors associated with shorter TTT. These factors formed a prognostic model identifying three groups: low 59% (median TTT 6.34 years), intermediate 36% (median TTT 4.08 years), high risk 5% (median TTT 1.49 years) (p < 0.001). There was a higher incidence of serious complications among risk groups (low 7.5% vs. intermediate 13.3% vs. high 25%; p = 0.096). The prognostic value of the LTB-TREAT model was confirmed in an external validation cohort. The low-risk group is predicted to have a prolonged TTT with WW and a high-risk group is predicted to experience early progression in whom treatment should be considered.