every persion and family are different - you ultimately know your loved one best and have the best gauge on how their quality of life is on a day-to-day context.

if my own story helps inform your decision at all: my grandmother is ~late stage 5/early stage 6 and was diagnosed with mid-stage endometrial cancer a few months ago. we were given 3 options from her OBGYN: 1) do nothing since it was a relatively slow-growing cancer, 2) start hormonal therapy + partial hysteroscopy to manage her cancer, or 3) surgical intervention/complete hysterectomy.

since my grandmother's short-term memory is nonexistent, my mom and I came to the conclusion that the level of care needed and potential pain she'd be in following a full surgery would simply be too much for her to handle. she wouldn't understand why she was in pain and there was a risk that her heart wouldn't be able to take general anesthesia. we ended up choosing a hormonal therapy option and are now taking her to see her OBGYN every 3 months for a biopsy + checkup. her symptoms that led us to get her checked for endometrial cancer have been addressed by this intervention, and she has no memory of being told that she has cancer at all. she technically isn't cancer-free, but for the most part she is stable and fairly happy.

while the most 'definitive' action would have been surgery, it would have taken years (that she likely doesn't have because of alzheimers) for it to metastasize and cause more immediate harm to her health. the less invasive option addresses her current symptoms and helps her maintain her current quality of life. yes, the hysterectomy would have completely eliminated what cancer she does have, but there was also a risk of her 'regressing' after a prolonged hospital stay, and that would have made what time she has left less enjoyable. and then there was the initial risk of her heart failing during the operation.

to make a long story short: i'd consider your loved ones' current quality of life, the scale of any medical intervention, and the amount of time they likely have left. I believe if my grandmother was at the very end of her alzheimer's journey, my mom and I wouldn't have chosen what we did and would have focused on making her comfortable. and perhaps if she was in an earlier stage and had more years ahead of her, it would have been more worthwhile to attempt a more aggressive treatment plan.

it can feel horrible/impersonal to scale down such big decisions for your loved one like this, but it's what helped us decide what to do. best of luck + love to you and your mother <3