Progress on Pseudoprogression

Well known as the most aggressive skin cancer, melanoma has a high likelihood of spreading to other parts of the body. The American Cancer Society estimates that over 9,300 people in the United States will die of metastatic melanoma this year (1). The standard of care for treating patients with metastatic melanoma is immunotherapy; an antibody to the immune checkpoint protein PD-1 is administered alone or in combination with other immunotherapeutic drugs.

Approximately one in 10 patients who receive this treatment experience a phenomenon called pseudoprogression, wherein immune cells infiltrating the tumor cause an increase in its size, mimicking the appearance of true disease progression. Radiologically, pseudoprogression can be identified by tumor enlargement or the development of new lesions, followed by shrinkage as the patient responds to continued treatment. In contrast, true progression can be seen when the tumor continues to grow and the patient remains unresponsive to immunotherapy.