Introduction:  One of the most important prognostic factors in breast cancer is metastasis to regional lymph nodes resulting in a reduced overall survival rate. Mast cells in tissue release both pro-tumourigenic and antitumourigenic substances and can determine progress of the tumour including invasion and metastasis. The present study endeavored to assess mast cell density (MCD) in regional axillary lymph nodes in cases of carcinoma breast with clinicopathological correlation to infer their biological role and pathological significance. Methods: Tissue from forty seven cases of invasive carcinoma of breast (mastectomy with regional axillary lymph node clearance) was analyzed and routine histological findings were recorded. Mast cells were clearly demonstrated in tissue using Toluidine Blue stain at pH 2.3. Mast cells were counted using an eyepiece grid and expressed as no. of cells / per sq. mm, i.e., mast cell density (MCD). The distribution of mast cells within all the sampled lymph nodes (with and without metastasis) was recorded. Results:  Mast cell density was statistically significantly (p<0.0001) increased in regional axillary lymph nodes without microscopic metastatic deposits (n= 255; Mean MCD +/- SD:  6.0 +/- 3.4) compared to lymph nodes showing metastatic deposits (n=140; Mean MCD +/- SD: 0.57 +/- 0.59). Conclusions: Our results indicate a clear anti-tumourigenic role of mast cells within the regional lymph node tissue in carcinoma breast, possibly limiting the mechanisms for invasion of lymphoid tissue and limiting the metastasis. Mast cell density could thereby be a significant prognostic indicator in the management of patients with breast carcinoma.

Keywords: Breast Carcinoma; Lymph Node; Mast Cell; Metastasis; Toluidine Blue.