A Case of Isolated Myeloid Sarcoma Associated With Germline EGFR T790M Variant: The Importance of Recognizing Potential Germline Variants on Somatic Tumor Sequencing Panels.

Isolated myeloid sarcoma is an uncommon subtype of acute myeloid leukemia associated with variable prognosis. We present the case of a previously healthy 30-year-old man presenting with chest pain and weight loss who was found to have a large mediastinal mass. Biopsy of the mass was consistent with isolated myeloid sarcoma. A somatic tumor sequencing panel revealed an EGFR T790M variant, which was later confirmed to be of germline origin. Germline EGFR T790M variants are associated with a hereditary predisposition to lung cancer, though myeloid malignancies have not yet been described. To our knowledge, this is the first reported case of myeloid sarcoma in a patient with an underlying germline EGFR T790M mutation. As somatic tumor sequencing panels become more commonplace, it is important to recognize potential germline variants in order to facilitate appropriate referral for genetic counseling, perform confirmatory genetic testing, and to develop a personalized treatment and surveillance plan for patients and their families.