A decrease in peripheral thyroid hormone conversion efficiency in patients treated with immune checkpoint inhibitors and L-T3 as a possible alternative therapeutic escape option.

Hypothyroidism is a frequently occurring side effect in patients under treatment with immune checkpoint inhibitors (ICIs). Actually, the origin of hypothyroidism with ICI use is classified as a primary (thyroid) or as secondary/tertiary hypothyroidism (hypothalamus-pituitary). Treatment consists of levothyroxine (L-T4) substitution.