Some very good advice already given and based on a sensible approach to the matter.
When I submitted an application to the DVLA to have my Cat D (buses) entitlement reinstated at age 70, it was accompanied by a medical report from my GP who stated I had PCa (along with a half dozen other conditions).
They wrote back to my GP and asked him to clarify a number of things relating to my conditions among which was a question on how advanced was my PCa and did my GP believe it would affect my brain or nervous system by way of metastasise in the foreseeable future. Given I'm a Gleason 6 on AS and low PSA (1.9) he responded accordingly and my licence was issued.
Interestingly the DVLA's GOV.UK site states:
You do not need to tell DVLA if you have cancer, unless:
- you develop problems with your brain or nervous system
- your doctor says you might not be fit to drive
It appears from the above you have no reason to advise the DVLA of the fact you have cancer unless you have developed the proscribed problems or your doctor says you might not be fit to drive.