Response of factor X deficiency to darutumumab in the treatment of AL amyloidosis: a novel finding.

We report a case of progressive light-chain amyloidosis (otherwise known as AL amyloidosis) with acquired factor X (aFX) deficiency with a complete haematological response and rapid normalisation of FX levels following daratumumab monotherapy. To our knowledge, this is the first case report documenting successful treatment with daratumumab of aFX deficiency secondary to AL amyloidosis. The patient responded well to this therapy, with excellent symptomatic and quality of life improvements as well as a reduction in bleeding manifestations. This case highlights the value in considering daratumumab treatment when AL amyloidosis is complicated by FX deficiency.