Dabrafenib and Trametinib With Radiosurgery in Melanoma Brain Mets

This is a single arm Phase II clinical trial. All patients will receive continuous dosing of dabrafenib at 150 mg PO bid and trametinib beginning at Cycle 3 Day 1, at a starting dose of 2 mg PO once daily until progression of disease, withdrawal of consent, or the development of intolerable treatment associated toxicity. An MRI will be performed after 28 days of treatment with dabrafenib. Patients who have unequivocal disease progression in the brain at that time will be deemed to have disease progression at 4 weeks. Patients with a complete response of all lesions in the brain will continue to receive dabrafenib and trametinib on study but they will not undergo SRS. For patients with stable disease or partial tumor responses in the brain, Gamma Knife radiosurgery will be performed on treatment cycle 2, day 1 (+/- 3 days, 28 day cycle) using a stereotactic head frame and MRI imaging in accordance with FDA-approved procedures. Melanoma brain metastases Cutaneous melanoma is the most aggressive form of all skin cancers. Worldwide, it is currently expected that approximately 132,000 people will be diagnosed with melanoma each year and some 37,000 people are expected to die of the disease annually. Brain metastases are a major source of morbidity and mortality in patients with metastatic melanoma and approximately 3 out of 4 develop brain metastases at some point in their disease course. The prognosis of metastatic melanoma with CNS involvement is dismal1, and, until recently, no medical therapy demonstrated clear evidence of activity against melanoma in the brain. For patients with fewer than 4 brain lesions and no brain lesion greater than 3 cm in diameter, stereotactic radiosurgery (SRS) is the standard-of-care. By delivering highly focal irradiation to melanoma brain metastases, SRS confers local control rates exceeding 80% for lesions under 2 cm in diameter. However, SRS does not treat micrometastatic disease in the brain, and new brain metastases develop in approximately half of patients treated. Furthermore, local control rates are lower for lesions larger than 2 cm in diameter. As a result, the median overall survival for melanoma patient treated with SRS is only 7 months. BRAF mutant melanoma The RAS/RAF/MEK/ERK pathway is a critical proliferation pathway in many human cancers. This pathway can be constitutively activated by alterations in specific proteins, including BRAF, which phosphorylates MEK1 and MEK2 on two regulatory serine residues. Approximately 90% of all identified BRAF mutations that occur in human result in a V600 E/D/Kamino acid substitution. This mutation appears to mimic regulatory phophorylation and increases BRAF activity approximately 10-fold compared to wild type. BRAF mutations have been identified at a high frequency in specific cancers, including approximately 40-60% of melanoma. The frequency of this activating mutation and the pathway addiction to which it leads makes mutated BRAF an extremely attractive target.