Predictive factors of response to immunotherapy—a review from the Spanish Melanoma Group (GEM)

Immunotherapy has become a key element in the treatment of several tumors, such as lung carcinoma and melanoma. Immunotherapy, unlike classical chemotherapy and targeted drugs, may yield long-term survival, even in patients who stop treatment due to toxicity. This fact has generated considerable excitement and a real shift in the paradigm of cancer treatment. However, only a small subset of patients benefit from immunotherapy. Survival curves show that most patients have progression of the disease in the first months after starting immunotherapy, followed by a slower decrease over the first 3 years, until curves reach a plateau. This early progression suggests the presence of mechanisms for primary resistance. In addition, some patients have tumor relapse after years of response, suggesting that there is also acquired resistance in a small subset of patients. Resistance mechanisms are now being elucidated. PD-L1 expression in tumor and immune cells correlates with higher chances of response, but melanoma patients with PD-L1 negative tumors can also respond. Several studies have demonstrated an increased probability of clinical benefit when tumors are infiltrated by CD8 T cells, have a high mutation burden or have an interferon gamma signature. But none of these factors has been implemented in the clinical practice, since more studies confirming their value are needed, as well as the development of standardized techniques.