Exceptional response to vemurafenib and cobimetinib in anaplastic thyroid cancer 40 years after treatment for papillary thyroid cancer

Case description: We present an unusual case of a patient that developed anaplastic thyroid cancer 40 years after treatment for papillary thyroid cancer. The patient presented with locoregional recurrence and distant metastasis. Tumor genotyping identified a BRAF V600E mutation. The patient was treated with drugs targeting BRAF V600E and MEK (vemurafenib and cobimetinib, respectively). The patient had a remarkable response with the right neck tumor shrinking 81% in size and disappearance of the distant metastases over an 8-month period. The patient underwent surgical resection of the residual tumor with genetic testing of the specimen showing persistent BRAF V600E mutation population of cells. Conclusion: Targeted drug therapy has been used with discretion on a case-by-case basis for anaplastic thyroid cancer and may result in good tumor response.