Successful outcome with oral sirolimus treatment for complicated lymphatic malformations: a retrospective multicenter cohort study.

Purpose: Sirolimus has emerged as a safe and effective treatment for complicated lymphatic malformations (LMs). We aim to prove the effectiveness and safety of sirolimus as a therapeutic option for patients with complicated LMs.

Methods: Fifty-eight patients with complicated LMs treated with sirolimus for at least 6 months at multicenter between July 2018 and January 2023 were enrolled. All patients were administered oral sirolimus starting at 0.8 mg/m² every 12 hours, with target serum concentration levels of 8-15 ng/mL. Evaluation for clinical symptoms and LMs volume on MRI were reviewed to assess treatment response and toxicities. Evaluation of disease response was divided into 3 values: complete response, partial response (significant, moderate, and modest), and progressive disease.

Results: The median age at the initiation of sirolimus treatment was 6.0 years (range, 1 month-26.7 years). The median duration of treatment was 2.0 years (range, 6 months-4.4 years). The most common lesions were head and neck (25 of 58, 43.1%). Forty-six patients (79.3%) demonstrated a reduction in LMs volume on MRI or improvement of clinical symptoms including 2 complete responses. The young age group and the patients who underwent few prior therapies showed better responses. None of the patients had toxicities attributable to sirolimus with a Common Terminology Criteria for Adverse Events grade of ≥3.

Conclusion: Oral sirolimus treatment brought a successful outcome without severe adverse effects. It could be the first-line therapy, especially for the young age group of complicated LMs, and an additional option for refractory lesions that did not respond to conventional treatment.