Successful treatment with dacarbazine against a parathyroid hormone-related protein-producing melanoma causing hypercalcemia after immune checkpoint inhibitor failure.

Cancer-associated hypercalcemia commonly occurs through abnormal secretions of parathyroid hormone-related protein (PTHrP) from cancer cells. Several cases of PTHrP-producing melanoma causing hypercalcemia have been reported; however, effective management of PTHrP-producing BRAF wild-type melanoma causing hypercalcemia after immune checkpoint inhibitor (ICI) failure is unclear. We report a case of PTHrP-producing BRAF wild-type melanoma leading to oncological emergency by hypercalcemia that was successfully treated with dacarbazine after ICI failure. A 65-year-old Japanese woman had advanced BRAF wild-type melanoma that was refractory to ICI, and then led to hypoxia through exacerbated lung metastases and pleural effusion. Moreover, hypercalcemia appeared in parallel with increase of the serum PTHrP level. Dacarbazine was administered, and after the first administration, the pleural effusion was gradually decreased and hypoxia rapidly disappeared, and the serum calcium and PTHrP levels were improved within normal limits. Dacarbazine after ICI failure is potentially a useful option for oncological emergency due to progression of BRAF wild-type melanoma including PTHrP-producing types. Dacarbazine should be reevaluated as a therapeutic option for oncological emergency in patients with BRAF wild-type melanoma after ICI failure.