Failure of second challenge with mogamulizumab in C-C chemokine receptor 4-positive cutaneous T-cell lymphoma

We report three patients with Sezary syndrome who had previously been successfully treated with mogamulizumab and then failed a second course of the same treatment, despite positive CCR4 expression at the second initiation of mogamulizumab. This suggests that secondary resistance of blood disease to mogamulizumab may be independent of target expression.