Discussion:
We report a case of synchronous p16+ SCC involving the BOT and
nasopharynx. To our knowledge, this is one of only two reports of
synchronous HPV associated SCC involving the oropharynx and
nasopharynx(3). There are however, reports of metachronous p16+/HPV+ NPC
diagnosed following prior OPC treatment, raising the possibility of
occult primaries lying within the nasopharynx in these cases (2).
This case presented a diagnostic dilemma. There was not uniform
agreement at our multi-disciplinary meeting and it was questioned
whether the initial biopsies had been mislabelled given the panendoscopy
(and negative biopsy) and MR findings of an obvious tumour in the BOT.
Although the FDG-PET/CT showed an abnormality in the nasopharynx, there
was no corresponding structural abnormality and false positive
FDG-PET/CT findings in the head and neck are well documented (4). The
repeat panendoscopy and PET/CT with corresponding reduction in SUV
further challenged the presence of a nasopharyngeal primary, but
nasopharyngeal adenoidectomy was felt to be prudent given a degree of
uncertainty, which confirmed a synchronous p16+ NPC.
While treatment of the nasopharynx was possible from the outset,
treating both the BOT and nasopharynx without sufficient proof will
almost certainly subject a patient to excessive long-term toxicities,
including lifelong dysphagia and possible feeding tube dependence.
Indeed, in this case a mean dose of 62Gy was delivered to the pharyngeal
constrictors which is associated with higher chances of long term
swallowing problems (5). In contrast, failing to treat the nasopharynx
at the outset would likely lead to an unsalvageable recurrence. Just
like the proposed recommendation by McGovern et al, we also recommend
care full physical examination and biopsies in case of increased uptake
on PET scan (3). While synchronous or metachronous p16+ OPC and NPC are
rare, it is also possible that the elective coverage of level two,
retropharyngeal and retrostyloid nodes will result in a dose wash
through the nasopharynx which might be sufficient to eradicate
microscopic disease.
International consensus guidelines on radiotherapy target volumes exist
for both NPC and OPC. There are however, no guidelines on the optimal
management of synchronous p16+ primary HNC. While OPC cases are
typically treated with isometric expansions (5+5mm) from gross disease
with elective coverage of nodal volumes, NPC treatment paradigms are
largely based on outcomes from EBV+ cases, mandating widespread elective
coverage of the base of skull. Whether this wide field coverage is
necessary in HPV+ NPC cases is not currently known, but warrants further
investigations.
In conclusion, we reported a unique case of synchronous p16+ SCC
involving both the BOT and nasopharynx. In the setting of a relatively
normal appearing nasopharynx on MRI, PET/CT may be useful in detecting
occult p16+ SCC in the nasopharynx and should guide more extensive
sampling, which may include adenoidectomy in selected patients.