Near Complete Response to Trametinib Treatment in Histiocytic Sarcoma Harboring a Somatic KRAS Mutation.

Survival outcomes of patients with histiocytic neoplasms are poor, with no standard-of-care treatments available for these malignancies. Recent characterization of the genomic landscape of various histiocytic neoplasms have shown a predominance of activating driver mutations within the MAPK/ERK pathway (ie, BRAF, MEK, KRAS, MAPK, and NRAS). Subsequently, successful treatment of these malignancies with BRAF and MEK inhibitors has been reported. This report presents the first patient with histiocytic sarcoma harboring a somatic KRAS Q61H mutation who was subsequently treated to a near complete response with the MEK inhibitor trametinib. Due to patient preference, lack of standard of care treatments, and associated morbidity from head and neck dissection, initial disease reduction provided by trametinib therapy allowed for a less morbid resection. This case report highlights the utility of up-front next-generation sequencing and the efficacy of MEK inhibition in patients with histiocytic sarcoma harboring activating KRAS mutations.