Hi Amit, my dad had a recurrence on other side of neck just like your mother however it was after 2 years and a big one (6 cms, it probably went undetected for few months due to scar tissue and otherise also it was asymptomatic). His treatment started with Pallative Chemotherapy (TPF regimen), followed by Radical Neck Dissection and 60 gy/30 unilateral (one side of neck) external beam radiotherapy. Its been few weeks since completion of treatment and my father still having tough time due to re-radiation.

Re-radiation (Neck) is usually not a preferred mode of treatment as it presents several complexities and has significant impact on Quality of life. It is a difficult choice for doctor to make, especially if it is an early recurrence. My dad's doctors checked several times with us if he has already completed 2 years from his previous radiation before deciding to go for it.

Considering the reccurence, chemotherapy alone will not help (otherwise also gold standard is chemo-radiation) and that leaves us with surgery as the best option. The Onco surgeon may be able to get other suspicious tissue samples and mark the tumor bed (they did for my dad: tumor had invaded his Cartoid artery sheath and prevertebral muscles) to plan any further course of treatment including re-radiation.

Treatment failure does leave us with lots of questions but there are no definitive answers. As Eric said, focus on treatment and beat cancer for the second time.

If you need any further help or guidance, please feel free to PM me, will give you contact details.