Abstract: We identified five new trials in this update, bringing the total number of included trials to 12 (2300 participants; 2148 with cancers of the oral cavity). We assessed four trials at high risk of bias, and eight at unclear. None of the included trials compared different surgical approaches for the excision of the primary tumour. We grouped the trials into seven main comparisons. Future research may change the findings as there is only very low-certainty evidence available for all results. Five trials compared elective neck dissection (ND) with therapeutic (delayed) ND in participants with oral cavity cancer and clinically negative neck nodes, but differences in type of surgery and duration of follow-up made meta-analysis inappropriate in most cases. Four of these trials reported overall and disease-free survival. The meta-analyses of two trials found no evidence of either intervention leading to greater overall survival (hazard ratio (HR) 0.84, 95% confidence interval (CI) 0.41 to 1.72; 571 participants), or disease-free survival (HR 0.73, 95% CI 0.25 to 2.11; 571 participants), but one trial found a benefit for elective supraomohyoid ND compared to therapeutic ND in overall survival (RR 0.40, 95% CI 0.19 to 0.84; 67 participants) and disease-free survival (HR 0.32, 95% CI 0.12 to 0.84; 67 participants). Four individual trials assessed locoregional recurrence, but could not be meta-analysed; one trial favoured elective ND over therapeutic delayed ND, while the others were inconclusive. Two trials compared elective radical ND with elective selective ND, but we were unable to pool the data for two outcomes. Neither study found evidence of a difference in overall survival or disease-free survival. A single trial found no evidence of a difference in recurrence. One trial compared surgery plus radiotherapy with radiotherapy alone, but data were unreliable because the trial stopped early and there were multiple protocol violations. One trial comparing positron-emission tomography-computed tomography (PET-CT) following chemoradiotherapy (with ND only if no or incomplete response) versus planned ND (either before or after chemoradiotherapy), showed no evidence of a difference in mortality (HR 0.92, 95% CI 0.65 to 1.31; 564 participants). The trial did not provide usable data for the other outcomes. Three single trials compared: surgery plus adjunctive radiotherapy versus chemoradiotherapy; supraomohyoid ND versus modified radical ND; and super selective ND versus selective ND. There were no useable data from these trials. The reporting of adverse events was poor. Four trials measured adverse events. Only one of the trials reported quality of life as an outcome. Twelve randomised controlled trials evaluated ND surgery in people with oral cavity cancers; however, the evidence available for all comparisons and outcomes is very low certainty, therefore we cannot rely on the findings. The evidence is insufficient to draw conclusions about elective ND of clinically negative neck nodes at the time of removal of the primary tumour compared to therapeutic (delayed) ND. Two trials combined in meta-analysis suggested there is no difference between these interventions, while one trial (which evaluated elective supraomohyoid ND) found that it may be associated with increased overall and disease-free survival. One trial found elective ND reduced locoregional recurrence, while three were inconclusive. There is no evidence that radical ND increases overall or disease-free survival compared to more conservative ND surgery, or that there is a difference in mortality between PET-CT surveillance following chemoradiotherapy versus planned ND (before or after chemoradiotherapy). Reporting of adverse events in all trials was poor and it was not possible to compare the quality of life of people undergoing different surgical treatments.

Plain-language summary: We included 12 trials (five new for this update) that investigated the success of surgical treatment for oral cancers. The studies involved 2300 participants, 2148 of whom had mouth cancers. The trials included seven comparisons of different treatment options. None of them compared different surgical approaches for cutting out the primary tumour. The findings of the studies are mixed and it is not possible to draw firm conclusions about the optimal surgical approach for mouth and throat cancers. Surgical removal of the lymph nodes in the neck that appear to be cancer-free, at the same time as the cancer is removed did not seem to be associated with longer survival in two studies whose results were combined. Another study, however, suggested there may be a benefit of early neck surgery in terms of overall survival and 'disease-free survival' (length of time after primary treatment without signs and symptoms of disease). One study found cancer recurrence at or around the same site was less likely with the early surgery, while three other studies did not favour either treatment. There was no evidence that removal of all the lymph nodes in the neck resulted in longer survival compared to selective surgical removal of affected lymph nodes. One study evaluated use of a special scan (positron-emission tomography-computed tomography (PET-CT)), after a combination of chemotherapy and radiotherapy, to guide decisions about neck dissection, and found no difference in mortality (death) compared with undertaking a planned neck dissection before or after chemoradiotherapy. There were a number of other surgical approaches compared in the studies, but we were unable to use the results in this review. Although removal of lymph nodes from the neck is known to be associated with significant negative effects related to appearance and functions such as eating, drinking and speaking, the studies reported poorly on these side effects and did not measure quality of life accurately enough or in large enough numbers to be included in any of our analyses. The certainty of the evidence was very low as there were few studies for each comparison and they were at risk of bias because of the way they were designed. Some comparisons and outcomes had no useable results.