Dear Editor,

We read with great interest the case-control study by Yildiz Kabak et al. regarding home exercise in patients undergoing hematopoietic stem cell transplantation [1]. Although the limitations are presented by the authors, the effects related to exercise in quality of life and in the treatment of patients undergoing hematopoietic stem cell transplantations are extremely relevant to this population that keep growing worldwide [2].

However, the case-control study reported in the article has changed its original design at the moment of selection of participants and by performing an intervention. A case-control study is an observational study, usually retrospective, in whose participants are chosen due their outcomes and separated by exposition [3], in which the final objective is to identify an odds ratio relating exposure with outcome [4]. Yildiz Kabak et al.’s research aimed to determine the effectiveness of an individual exercise program by starting before hematopoietic stem cell transplantation and continued with home exercise program after discharge up to 100 days after transplantation. Being a prospective study, with an intervention group and without information about randomization, it seems to us that this research fits better as a prospective, controlled study [5].

Sincerely,

Laura Nogueira, B.Sc

Andrya Blazina, B.sc

Institute of Cardiology, University Foundation of Cardiology, Porto Alegre, Rio Grande do Sul, Brazil