Prognostic impact of intra-field heterogeneity in oral squamous cell carcinoma

Genetic heterogeneity displayed by tumour cells (intratumoural heterogeneity, ITH) represents a diagnostic challenge when assessing tumour mutational profile. In oral squamous cell carcinoma (OSCC), ITH may be found both in tumour cells and in adjacent mucosa. Genetic heterogeneity of the adjacent mucosa can be interpreted as evidence of the field cancerization (field heterogeneity, FH). The aim of the study was to investigate the impact of intratumoural and intrafield heterogeneity on locoregional control. Ten OSCC patients (5 recurrent and 5 nonrecurrent) were studied. Multiple areas were sampled from the bulk of the tumour and the adjacent nonneoplastic mucosa. A panel of 10 tumour-specific OSCC driver genes was analysed for each sample and was used to calculate heterogeneity. Values were compared among recurrent and nonrecurrent OSCC. Mutational analysis highlighted that a single tumour sample has limited accuracy in assessing the genetic profiles of tumours. High values of ITH considering shared mutations between specimens were found in both recurrent and non-recurrent OSCC (p = 0.095). On the contrary, the intrafield genetic heterogeneity was significantly less frequently in the non-recurrent OSCC group (p = 0.032). Heterogeneity within each specimen calculated with variant allele frequency confirmed that there was better discrimination between recurrent and nonrecurrent groups using nonneoplastic adjacent mucosa than tumour tissue (p value 0.0006 and 0.0048 respectively). In agreement with the theory of field cancerization, intrafield genetic heterogeneity correlates with a higher risk of developing loco-regional recurrences and second primaries. In order to reduce the ITH effects, analysis of multiple tumour areas should be encouraged.