Association of quantitative assessment of the intrafollicular proliferation index with outcome in follicular lymphoma

Summary: The role of the proliferation index (PI) as an outcome predictor in follicular lymphoma (FL) isn't clear. We have previously demonstrated that quantitative image analysis (QIA) is a robust tool for PI determination and the present study aimed to determine the significance of the PI for outcome in low-grade FL. One hundred and twenty-nine patients with grade 1-2 FL were retrospectively analysed. Slides were scanned digitally and follicle/tumour-involved areas were annotated. The intrafollicular PI was estimated by analysing a median of 10 follicles per case. Patients were divided into two groups: PI < 30%, PI ≥ 30% and clinical outcome was analysed. Among the 129 patients analysed, intrafollicular PI ranged from 0·6 to 63·2% with a median of 23·3%. Overall survival was not influenced by PI group. Among those patients initially observed, intrafollicular PI < 30% was associated with longer time to first therapy compared to patients with a PI ≥ 30%. In the group of patients that were treated at diagnosis, PI was not predictive of time to treatment failure (TTTF). Intrafollicular PI is an important predicator of TTFT for patients who are candidates for observation. Further confirmation in an independent cohort of patients is necessary to determine the clinical validity of the results.