Koos Boeve

115 Cyclin D1 in early oral cancer Cyclin D1 expression did not correlate with unfavorable growth patterns, which is in line with other studies, although some studies found a correlation with differentiation grade in oral cancer [27,28]. However, it must be realized, that the benefit of the biomarker lies in its preoperative application on the incisional biopsy: to decide whether or not to perform a neck dissection at the same time when resecting the primary tumor. Reliable acquisition of the histological tumor characteristics can only take place after the ablative surgery [29]. CCND1 high-level amplification was significantly correlated with higher nuclear cyclin D1, although not all amplified tumors showed high cyclin D1 expression and some tumors showed high nuclear cyclin D1 staining without amplified CCND1 . These inconsistencies between genomic alterations and protein expression levels are in line with earlier reports in breast and head and neck cancer and could be explained by regulation of transcription, translation and protein stability [30,31]. This study has been performed in a clinically relevant large consecutive cohort of early oral cavity SCC. However, some limitations have to bementioned. First, both IHC and FISH analysis have been performed on resection specimens. Although this allowed us to investigate intratumoral heterogeneity, which is essential for potential biomarkers, it is relevant to validate these findings for incisional biopsies as well, to confirm its diagnostic value in daily clinical practice. Second, not all included patients underwent the same treatment of the neck. The majority received an elective neck dissection, in which micrometastasis could be missed [32]. In twenty-three percent of our cases, definitive status of the neck was established by follow-up of at least two years. All nodal metastases during follow-up have been confirmed by ultrasound with FNAC or histopathological examination of the resection specimen after a therapeutic neck dissection. Although one patient with watchful waiting in our group received postoperative irradiation of the primary tumor, we believe the amount of bias this caused is minimal. Third, as already mentioned, the cohorts used for validation are prone for selection bias as only patients treated with a neck dissection were included. In conclusion, this study identified cyclin D1 expression as a highly sensitive biomarker for occult nodal metastasis in early FOM oral cavity SCC with a NPV of 95%, which seems to be at least as accurate as the SNB is at this site of the oral cavity. As the intratumoral heterogeneity of this biomarker is minimal, this should make cyclin D1 expression in an incisional biopsy representative for the complete tumor. Furthermore, reproducibility of the cyclin D1 expression outcome is shown by the high interobserver agreement. Although the correlation with occult nodal metastasis in FOM tumors was still significant in our validation cohort, the NPV lowered to 79%, potentially because of selection bias. For this reason, its value as a diagnostic biomarker should be validated in a prospective study on incisional