Tumour-associated macrophages in diffuse large B-cell lymphoma: a study of the Osaka Lymphoma Study Group

Aims: To evaluate the role of tumour-associated macrophages (TAMs) of the M1 and M2 types in the behaviour of diffuse large B-cell lymphoma (DLBCL). Methods and results: Double immunohistochemical staining of HLA-DR/CD68 (M1) or CD163/CD68 (M2) was performed in 101 cases of DLBCL. CD68+ cells represent the total number of TAMs. The average number of double-positive cells was counted, and the cut-off value was set at the mean number of counts, i. e. 30.7 and 27.0 for M1 TAMs and M2 TAMs, respectively. That for total TAMs was set at the 90th percentile number of total counts, i. e. 132.3. Cases were categorized into three pairs: high (34 cases) and low (67 cases) M1 TAM groups, high (39 cases) and low (62 cases) M2 TAM groups, and high (10 cases) and low (91 cases) total TAM groups. The difference in overall survival rates was statistically significant between the high and low M2 TAM groups (P < 0.01) and between the high and low total TAM groups (P < 0.05). Multivariate analysis revealed that the presence of a bulky mass and a higher number of M2 TAMs were significant factors for poor prognosis (P < 0.05). Conclusions: Estimation of specific type of macrophages, of the M1 and M2 types, is superior to the estimation of TAMs as a whole (CD68+ cells) for prediction of the prognosis of DLBCL patients.