A new local treatment option in recurring tumours
Recurrent head and neck cancers (HNC) occur in 50-60% of patients within 2 years of initial successful treatment of the index head and neck cancer. It can also occur as a secondary primary malignancy (SPM) histological and geographically distinct from the index HNC, due to “field cancerization”. [1,2] In both scenarios, management of these cancers can be challenging, as standard of care treatments such as repeat surgery and/or radiation may not be possible due to the prior surgery with altered anatomy or radiation dose limits. As such, many patients will receive systemic treatment for a localized disease due to lack of suitable loco-regional treatment options. Consequently, these patients portend a poor prognosis, as they tend to be biologically less favourable given the recurrent or secondary nature of the tumour. Therefore, ablation with curative intent, which is commonplace elsewhere in the body such as the liver and kidney, is seldom possible, and a palliative intent is an acceptable treatment endpoint, e.g. aiming for local control, palliation of mass effect, pain management, and delay of oro-aero-bypasses (e.g. PEG/tracheostomies).
Using the “big five” to face challenging anatomy
The body of literature describing local ablation of HNC remains limited, consisting of mainly case series.  However, physicians have been apprehensive to widely adopt this technique, partly due to the complex anatomy inherent to the HN region, especially in the post-surgical neck. To this end, a standardized approach to reach the different deep spaces of the HN region has been recently described to overcome this technical hurdle.  To summarise, five different relatively avascular trajectories allowing for safe access to the deep spaces have been described based on the appearance of bony and soft-tissue landmarks on axial CT. These are: sub-zygomatic, retro-maxillary, retro-molar trigone, trans-glandular, and trans-flap. In addition, a hybrid approach has also been undertaken in areas that could be reached under direct vision and ablation guided using endoscopy and intra-operative ultrasound, such as tumours in the oropharynx and nasopharynx.
What to watch out for
In both the percutaneous or hybrid approach, protection of organ-at-risk (OAR) is crucial. Relevant OAR would include the carotid artery which beyond haemorrhage/blow-out and stroke risk if inadvertently injured, could also cause intra-operative autonomic instability due to neural pathway thermal disturbance. Destruction of cranial nerves in the vicinity of the tumour are typically acceptable during ablation, as loss of function is expected with disease progression (without treatment) or would be destroyed with other local treatment (e.g. enbloc resection or radiation). Other OAR would include the glossus, orbital contents, and brain which would either require physical displacement (e.g. hydrodissection) or real-time monitoring of the ablation zone.
To conclude, ablation can potentially fulfil a treatment gap in patients with recurrent HNC tumours who often have limited treatment options. A systemic technical approach and awareness of relevant issues can allow for a safe procedure with minimal anxiety.