Summary

Follicular lymphoma (FL) is the most common indolent lymphoma. Currently there are many comparable treatment options available for FL. When selecting the most optimal therapy it is important to consider possible late effects of the treatment as well as survival. Secondary haematological malignancy (SHM) is a severe late effect of treatments, but the incidence of SHMs is still largely unknown. The goal of the present study was to determine the incidence of SHMs and how therapeutic decisions interfere with this risk. The study included 1028 FL patients with a median follow‐up time of 5·6 years. The 5‐year risk of SHM was 1·1% and the risk was associated with multiple lines of treatment (P = 0·016). The 5‐year risk of SHM was 0·5% after the first‐line treatment and 1·6% after the second‐line. The standardized incidence ratio (SIR) was 6·2 (95% confidence interval 3·4–10·5) for SHM overall. This retrospective study found that the risk of SHM was low after first‐line treatment in FL patients from the rituximab era. However, the risk of SHM increases with multiple lines of treatment. Therapeutic approaches should aim to achieve as long a remission as possible with first‐line treatment, thereby postponing the added risk of SHM.