Not quite the same as your situation, but...in case it helps you and other forum members...
I had booked a flight before I was diagnosed, however I hadn't taken out travel insurance since the flight was booked months and months ahead and I wasn't expecting to get cancer, let alone so young!
Initially I was hoping to be well enough, since it was after end of active treatment, but then got complication of bad anaemia to the level where oxygen would be an issue if I flew. Clearly I wasn't going anywhere!
I phoned the flight company who informed me that;
a/ if I had insurance I should go to the insurer first, and,
b/ if I had no insurance or my insurer would not cover the flight, they would refund me the cost of the flight (or let me use the £ on another flight within a year) if my GP provided a letter explaining the condition and that I was unfit to fly and if I agreed to get a medical certificate that I was fit to fly if I flew with them in the future.
I can only say I was pleasantly astounded when they reimbursed me, not to mention extremely grateful.
I have no idea if this was a rare, one off approach, or if some airlines, perhaps to avoid health and safety issues on board with a passenger who is definitely too ill to fly, may take a similar approach? It was in 2014 so it's possible their approach may have changed too. Please note the organisation concerned would only do this for me as the person too ill to fly, not for anyone accompanying (friends still went!)
The other thing would be to consider contacting the holiday company and asking if you could change the dates. I have no idea if they would, or perhaps might consider it for a fee given the circumstances?
I have used Eurortrain for European holiday insurance before, I think (from recollection) at the point you take out the insurance they ask you, if you had to claim, would your GP be able to state that you were fit to go on holiday/fly etc. Hence if during chemo Eurotrain may not be receptive given their policy - maybe a conversation with your GP may help inform this?
I hope that helps give a few ideas on potential routes and wish you all the best with the chemo.
I haven't been in the position you're in, as I did not need chemo, but from my experience of arranging travel insurance after completing treatment last year, I do remember terms & conditions clearly stating that any existing medical conditions must be declared, including any visits to the GP about any unrelated condition over the past 2 years, as well as cover only being granted on completion of treatment.
It may also be an idea to check cover on your other health insurance as well.
I have seen in here & read in the papers recently about a company 'Insurewith' (I think) that specialises in cover for those with a cancer diagnosis, so it maybe worth checking it out.
Sorry not to be a lot of help on this, maybe others will be able to help.
We have a holiday booked for between my last round of EC and first round of Taxol. My oncologist had originally said I should be fine to go, but my reaction to first EC was not great so I am now nervous about the risk of us having to cancel.
I was hoping to find some travel insurance that would cover us for any cancellations related to my chemo (I am less focused on being covered for problems while we are out there as I believe my normal healthy insurance covers us abroad as well).
So far I am not having much luck - everyone says no because I'm in the middle of treatment and that I wouldn't be covered for cancellation because it's a known diagnosis.
Has anyone tried to do this with more luck?