Role of pax-5 immunohistochemistry in haematolymphoid malignancies

Objective: Histomorphology and immunohistochemistry are essential tools for evaluation and classification of haematolymphoid malignancies. The present study was conducted with the aim to study and categorize various haematolymphoid malignancies in lymph node and bone marrow biopsies using routine H & E staining and IHC markers and to study usefulness of Pax-5 in differentiating various lymphomas and leukemias. Material and Methods: The present study was conducted in Department of Pathology at PGIMS, Rohtak. Seventy cases of haematolymphoid malignancy including lymph node biopsy and trephine bone marrow biopsy were included in the study. Various histomorphological changes were examined on routine H&E. Cases with provisional diagnosis of lymphoma/leukemia were further submitted to immunohistochemicalstaining for a panel of lymphoma/leukemia markers including Pax-5 immunohistochemical antibodies. A descriptive study was carried out for all the variables included in the study. Fischers exact test was used to compare the categorical values. P-value <0.05 was accepted as statistically significant. Results: Immunohistochemical expression of Pax-5 was detected in all cases of Diffuse large B-cell lymphoma (n=9), Small lymphocytic lymphoma (n=7), Peripheral B Cell Lymphoma-NOS (n=6), follicular lymphoma (n=5), mantle cell lymphoma (n=4), marginal zone lymphoma (n=1) and B cell-ALL (n=8). In Hodgkin Lymphoma, nuclear Pax-5 immunoreactivity was seen in 71.4 % (5/7) of cases.However, Pax-5 was not detected in any case of NHL-T cell type including Anaplastic Large cell lymphoma (n=2) and T cell-ALL (n=1), AML (n=9) and plasma cell neoplasm (n=4).One of the two cases of ALCL was initially kept with differentials of ALCL or cHL but was subsequently reclassified as ALCL based on negative Pax-5 immunoexpression. The expression of Pax-5 in all the cases was statistically significant.(p<0.05). Conclusion: Pax-5 is an excellent B cell marker with its immunohistochemistry being a valuable tool in the diagnosis and subclassification of haematolymphoid malignancies.