Most studies have reported an increasing risk of occult metastasis in the neck with increasing tumour depth of invasion and consequently, reduced recurrence-free overall survival.
This risk ranges from 20 to 30 percent 1-2. Assessing the depth of invasion of the tumour is extremely difficult without removing the entire tumour whilst a sample from a biopsy may not be representative of the entire lesion. In some cases, a staged approach where the tumour is removed first is entirely appropriate. A cut-off 3mm depth of invasion is now generally accepted as an indication to carry out an elective neck dissection incorporating ipsilateral neck levels one to three ( including level four for tongue cancer), with dissection of an additional neck level where there is presence of tumour at that level.
This is based on a large, prospective randomised controlled trial3 in which 596 patients were randomly assigned to:
- Elective neck dissection
- Observation followed by elective neck dissection for recurrence.
After a median follow-up of 39 months the results were:
- Elective neck dissection group: 81 recurrences and 50 deaths
- Observation followed by elective neck dissection for recurrence: 146 recurrences and 79 deaths.
In summary, three year overall survival was significantly improved in the elective dissection group (80 vs 67.5 percent) as well as overall survival ( 69.5 vs 45.9 percent) therefore, all stage I oral cavity cancers with a depth of invasion greater than 3mm should have:
- An ipsilateral neck dissection for well lateralised tumours.
- A bilateral neck dissection for tumours close to the midline,
- Pentenero M, Gandolfo S, Carrozzo M. Importance of tumor thickness and depth of invasion in nodal involvement and prognosis of oral squamous cell carcinoma: a review of the literature. Head Neck 2005; 27:1080.
- Huang SH, Hwang D, Lockwood G, et al. Predictive value of tumor thickness for cervical lymph-node involvement in squamous cell carcinoma of the oral cavity: a meta-analysis of reported studies. Cancer 2009; 115:1489.
- D’Cruz AK, Vaish R, Kapre N, et al. Elective versus Therapeutic Neck Dissection in Node-Negative Oral Cancer. N Engl J Med 2015; 373:521.