Discussion
This study examines the distribution of clinically known and occult
nodal disease in neck dissection specimens of patients with p16+ve OPSCC
who have undergone primary treatment with TORS/TOLM and ND. The data
reaffirms previously reported data on the importance of including levels
II, III and IV in ND for any cN+ve p16+ve OPSCC, although the volume of
previously published literature is low 9-11. The
frequency of occult node metastasis in patients staged overall as cN0
(four of nine NDs, 44%) underlines the importance of sound oncological
surgical technique when undertaking selective neck dissection in this
cohort. There is no place for limiting the neck dissection to levels II
and III; levels II, III and IV is the minimum neck dissection patients
should be offered regardless of the absence of clinical disease in prior
echelon levels.
Three other studies previously published have examined the nodal
distribution specific to p16+ve disease 9, 10, 12,
with just one comparing the breakdown of clinically known and occult
nodes 10. Previous studies had examined the
distribution pattern of known and occult OPSCC nodal disease
irrespective of p16 status,4, 13-17 with HPV only
relatively recently demarcated as a disease subtype with a specific
natural history and transmission.3 A recent Zenga et
al. study examined a cohort of 324 pN+ve p16+ve OPSCC patients; however
this study did not assess the distribution of LNs by neck
level.11
The data we report here is consistent with studies reporting the
frequency of occult lymph node metastasis in equivalent patient groups
in level II (24-80%), level III (0-60%), and level IV nodes
(0-27%).4, 10, 15, 17 The reported frequency of all
LN metastasis are 76-90% for level II, 22-50% for level III and 9-14%
for level IV which are comparable with our data. 4, 9,
10, 12, 13, 17. The insight gained from this study is similar to
Amsbaugh et al who compared nodal distribution frequency in p16+ve and
p16-ve OPSCC,12 but which only examined the
distribution of cN+ve LNs. This found that the distribution of nodes in
p16+ve disease was not significantly different to an historical
Lindbergh study on overall nodal distributions in OPSCC conducted prior
to establishment of the HPV aetiology.13 However, the
Amsbaugh et al study had a 67% rate of smokers, introducing a
confounding risk factor compared to our cohort with only 39% of
patients reporting as current or significant smokers in the past.
We acknowledge that there is a weakness in our reporting of level IIA
and IIB disease as this was only available for a small subset of
patients (table 2), however with the limited data available we have
shown that the presence of level IIB disease was always associated with
level IIA disease. Generally, the senior authors’ policy is to dissect
level IIA and IIB as standard in this patient group, but these specimens
have, for the majority, been sent as a single level II specimen without
sub-division. A larger study found isolated IIB disease in 2.2% without
level IIA disease, although none in cN0 necks.4Recommendations in the United Kingdom remain that IIB can be left intact
in T1-2 tumours if clinical disease in IIA is absent,3,
4 with heightened suspicion in tonsillar tumours.4
As with this study, previous reports on occult nodes for NDs reported
uncommon involvement of levels I and V, with frequencies of 0-9% for
level I and of 0-7% for level V.4, 10, 14, 15Dissection of level I is not considered routine and is advised in the
presence of anterior tumour expansion into the oral cavity or in the
presence of cN+ve level I lymph nodes.3