Uncovering the ultra-frail: A distinct subgroup in non-transplant eligible newly diagnosed patients with multiple myeloma, with an inferior clinical outcome.

Kazimierz Groen, Febe Smits, Kazem Nasserinejad, Mark-David Levin, Josien C Regelink, Gert-Jan Timmers, Esther G M de Waal, Matthijs Westerman, Gerjo A Velders, Koen de Heer, Rineke B L Leys, Roel J W van Kampen, Claudia A M Stege, Maarten R Seefat, Inger S Nijhof