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 selectively dissect the 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,
Sentinel lymph node biopsy may be considered for the contralateral neck and for tumours with less than 3mm depth of invasion.
- 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.