So it's been a while but I've been meaning to update this, and I've finally found the time.
First off, during the TURBT, the urologist decided to open up a bladder diverticulum (that had somehow had its opening blocked), and inside it he found another suspicious growth.
The samples were sent for biopsy, the results were pretty bad. The tumor outside was grade 1, the tumor inside the diverticulum was grade 3, which made us panic, since from my understanding, cancers in the diverticulum can skip muscle invasion and go directly to the next stage, which is super scary.
Our original Uro wanted to continue with BCG and do another 6 round induction.
I insisted we also get a 2nd (and 3rd) opinion and at least entertain the idea of RC.
We eventually went to an uro surgeon, who also performs RC. He made my father do a battery of tests (in preparedness for a very probable RC), and also get the biopsy samples and have a different lab look at them.
The results from the different lab were... different. The G1 tumor was diagnosed to be something non-cancerous (the exact diagnosis escapes me right now, I think some type of Fibroma but I may be misremembering) and the grade 3 inside the diverticulum was diagnosed to be "nephrogenic adenoma", which is a rare benign growth and quite possibly caused by the BCG instillations.
We did another round of TURBT (performed by the new uro that we visited for the potential RC) and additional samples were taken, and the diagnosis remained the same "nephrogenic adenoma".
So we stopped the BCG instillations. Which is a bit worrying, but hopefully the 18 doses (or so) of BCG my father has already done will be sufficient.
Since then we did a bunch more cystoscopies and cytologies in a monthly rate. The cytologies were pretty good (results showed a few "atypical" cells) and cystoscopies showed some red areas, which in subsequent cystoscopies seemed to shrink which indicated they are not something to worry about, and the last one, 2 and a half months ago, was clean, at which point it was decided we go back to the normal 3-month cystoscopy schedule.
So all in all, so far, this has turned out pretty good so far for my father. The BCG instillations were pretty hard on him and he was starting to get persistent prostatitis and bladder infections (which apparently can also be a cause for nephrogenic adenoma), which sent us to the hospital a couple of times a year+ ago (which during the height of COVID was extra chaotic).
He seems much healthier now.
Ideally he would be able to continue the BCG instillations, but I'll take being unable to do more BCG doses over having a high grade recurrence and having to rush to do a RC.
We have another cytology / cystoscopy coming up in a couple of weeks. I'm hoping for good results.
I would like to thank everyone on this forum. I haven't really been posting much, but there were periods where I was under a lot of stress and reading other people's stories and experiences made the whole thing a little less overwhelming.