MIB-1 proliferation index (PI) has proven helpful for diagnosis and prognosis in non-Hodgkin lymphomas (NHLs). However, validated cutoff values for use in fine-needle aspiration (FNA) samples are not available. We investigated MIB-1 immunocytochemistry as an ancillary technique for stratifying NHL and attempted to establish PI cutpoints in cytologic samples.
B-cell NHL FNA cases with available cytospins (CS) MIB-1 immunocytochemistry results were included. Demographic, molecular, immunophenotyping and MIB-1 PI data were collected from cytologic reports. Cases were subtyped according to the current World Health Organization classification and separated into indolent, aggressive, and highly aggressive groups. Statistical analysis was performed with pairwise Wilcoxon rank sum test and linear discriminant analysis to suggest appropriate PI cutpoints.
Ninety-one NHL cases were subdivided in 56 (61.5%) indolent, 30 (33%) aggressive, and 5 (5.5%) highly aggressive lymphomas. The 3 groups had significantly different MIB-1 PIs from each other. Cutpoints were established for separating indolent (<38%), aggressive (> or =38% to < or =80.1%) and highly aggressive (>80.1%). The groups were adequately predicted in 76 cases (83.5%) using the cutpoints and 15 cases showed discrepant PIs.
MIB-1 immunohistochemistry on CS can help to stratify B-cell NHL and showed a significant increase in PI with tumor aggressiveness. Six misclassified cases had PIs close to the cutpoints. Discrepant MIB-1 PIs were related to dilution of positive cells by non-neoplastic lymphocytes and to the overlapping continuum of features between diffuse large B-cell lymphoma and Burkitt lymphoma. Validation of our approach in an unrelated, prospective dataset is required.