The significance of minimal bone marrow (BM) involvement in diffuse large B cell lymphoma (DLBCL), as determined by flow cytometry (FC), is unclear. Patient outcomes were retrospectively analyzed based on their BM biopsy and FC involvement. Eighty-one patients were included, 21 and 51 were positive for biopsy(B+) and FC(FC+) respectively. B+ FC+ patients had a 52.3%CR rate, the B- FC+ group had 76.7%, and the B- FC- had 73.3%. Mean time to progression (TTP) was 67.45, 76.8, and 79.3 months and median Overall survival(OS) was 54.4, 76.6 and 69.5 months for the B+ FC+, B- FC+, and B- FC- groups respectively. A cutoff of 1% pathologic cells was an independent risk factor for TTP. In a multivariable analysis including International Prognostic Index (IPI), sex and HB, FC+ was independently associated with TTP (but not OS) at 5 years (HR 2.64, 95%CI 1.03-6.77) and at 7 years(HR 2.83, 95%CI 1.08-7.39). In summary, FC determined minimal involvement may suggest an intermediate risk group of DLBCL patients.
Keywords: Diffuse large B cell lymphoma; flow cytometry; minimal involvement; prognostication.