One study used a humanized mouse melanoma model wherein a combination of anti-PD-1 antibody with targeted tyrosine kinase inhibitor sunitinib or imatinib resulted in the complete tumour reversion associated with mast cell depletion, identifying both a possible source of resistance for cases where primary resistance to treatment is faced as well as the underlying pathway through which this process may occur [113]. The gene discussed is PDCD1; the disease is melanoma.