Clinical next-generation sequencing for precision oncology in rare cancers

The European Society for Medical Oncology defines rare cancers as 5 or fewer cases per 100,000 persons per year. For many rare cancers, no standard of care exists, and treatment is often extrapolated. Identifying potentially targetable genomic alterations in rare tumors is a rational approach to improving treatment options. We sought to catalog these mutations in rare tumors and to assess their clinical utility. For this retrospective analysis, we selected rare tumor patients from a dataset of patients who underwent clinical tumor genomic profiling. Sarcomas were excluded. To index potentially actionable alterations, patients' reports were reviewed for mutations in cancer-associated genes and pathways. Respective clinical records were abstracted to appraise the benefit of using a targeted therapy approach. Actionable alterations were defined as targeted by a drug available on-label, off-label, or in clinical trials. The 95 patients analyzed had 40 different tumor subtypes, most common being adenoid cystic (13%), cholangiocarcinoma (7%), and metaplastic breast (6%). At least one genomic alteration was identified in 87 patients (92%). The most common identifiable mutations were in TP53 (23%), KRAS (10%), PIK3CA (9%), CDKN2A/B (8%), BRAF (7%), MLL (7%), and ARID1A (6%). Thirty-six patients (38%) with 21 different tumors had at least one potentially actionable alteration. Thirteen patients received targeted therapy. Of these, 4 had a partial response, 6 had stable disease, and 3 had progressive disease as the best response. The addition of genomic profiling to management of rare cancers adds a potential line of therapy for cancers that have little or no standard of care. In our analysis, tumors with a BRAF alteration responded well to BRAF inhibitors.