Outcome and age distribution of Stage I FL cases. (A) Outcome of 28 cohort 2 Stage I FL patients (≥ 18 years of age). Patients with FL lacking BCL2 gene abnormality and with elevated Ki67 proliferation index (BCL2-N/HPI) demonstrated superior freedom from progression or relapse (median time not reached) compared with patients with FL bearing BCL2 gene rearrangement or gain (BCL2-R) or nonelevated proliferation index (LPI; median, 43 months). (B) Age distribution of stage I FL cases (cohorts 1 and 2).