It is noteworthy that the two Reunionese patients, who were infected with cytochrome b mutant P. jirovecii organisms, were effectively subjected to atovaquone prophylaxis in a context of hematological malignancy (myeloma for one patient, and T-cell acute lymphoblastic leukemia for the other), at the time of PCP diagnosis. The gene discussed is MT-CYB; the disease is T-cell acute lymphoblastic leukemia.