Understanding patterns of invasion: a novel approach to assessment of podoplanin expression in the prediction of lymph node metastasis in oral squamous cell carcinoma.

AIMS: Cellular motility is considered to be central to the process of metastasis, and podoplanin expression can be explored as a prospective link, owing to its ability to modulate the actin cytoskeleton. We aimed to evaluate the tumoral expression of D2-40 (monoclonal antibody against podoplanin) in pathologically neck-node-negative/positive cases (pN0/N+) to characterise the pattern of invasion, potentially explaining the role of various patterns of invasion in causing tumour metastasis.

METHODS AND RESULTS: Paraffin-embedded tissue blocks of 60 oral squamous cell carcinoma cases of known nodal status were selected for immunohistochemical staining of tumour (invasive front) by D2-40 along with routine staining by haematoxylin and eosin. Various staining patterns were assessed and evaluated for D2-40 expression, and correlated with nodal status. Tumoral D2-40 expression correspondingly increased with nodal metastasis (P = 0.261). Furthermore, D2-40 staining was more efficient in detecting individual tumour cells, and also characterised the motility factor irrespective of the pattern of invasion (P = 0.001). The pattern of D2-40 staining did not show a significant association with tumour grade, indicating that motility is an overlooked, albeit important, component of the pattern of invasion in routine histological grading.

CONCLUSIONS: D2-40 expression successfully identifies the motility profile of tumour, irrespective of the pattern of invasion. The presence of larger motile islands in the tumour cohort supports the concept of 'collective cell migration'. Podoplanin also aids evasion of immune responses by inducing platelet aggregation over tumour cells, thereby favouring distant metastasis. A multivariate model using immunohistochemical staining with D2-40 provides greater sensitivity for the prediction of lymph node metastasis.