Mitosis - predicting primary tumour and metastatic lymph node behaviour and beyond in OSCC - A pilot study.

Background and objectives: In the evaluation of oral cancer, mitotic index/mitotic figures are of paramount importance in histopathology. The number of mitoses in tumour cells is directly proportional to the activity of the tumour cells. In this novel study, we evaluated the status of the mitotic figures found in the metastatic deposit of the lymph nodes in addition to the primary tumour. A great deal of significance is given to this parameter in the evaluation of progress of the primary tumours in a state of distant metastasis. Therefore, we propose to analyse the lymph node mitotic index (LMI) in metastatic deposits and its relation to the primary tumour by assessing the relation between primary: LN mitosis ratio (PLMR). This also can provide an insight into the concept of understanding the dynamic state of lymph node deposits in oral squamous cell carcinoma (OSCC).

Materials and methods: A total of 510 lymph nodes from 17 cases of surgically treated OSCC were analysed, of which 40 lymph nodes were found to be positive. These 40 lymph nodes were examined histopathologically for the presence of mitotic figures in ten randomly selected fields (x400) and compared to the mitotic activity of the primary tumour by two observers independently, along with other histopathological features. LMI and PLMR were further determined for these cases.

Observations and results: The mitotic index was significantly higher in the metastatic deposits than in the primary tumour (P = 0.004). A higher percentage of abnormal mitoses was observed in metastatic lymph nodes, but no statistical significance (P = 0.27) was found when compared with primary tumour. Statistically significant correlation (P = 0.001) was observed between abnormal mitoses (%) and presence of ECS as well as size of the metastatic deposits. The LMI ratio showed a high mitotic rate in close to 80% of the cases. PLMR showed 58-60% cases with mitotically more active lymph nodes.

Interpretation and conclusion: This study is the first of its kind, which examines a level further than the nature of the primary tumour. Mitotic index/numbers in lymph nodes (LMI) might be considered an important parameter to evaluate the disease spread, revealing the nature of transiently indolent and mitotically active metastatic lymph nodes. The PLMR adds a further dimension on the lymph node's dynamic status in the progression of the disease.