Fatigue will drive sexual desire into the ground. When people are going through any kind of chemotherapy or radiation or following surgery, they need to be flexible. If they are not feeling sexual desire they need to remind themselves that fatigue and going through treatment is very difficult. They need to be very kind to themselves and to rest a lot, and try to move any kind of sexual interaction to a time of the day when they feel more energetic. The second main concern would be difficulty feeling arousal because of the general drying effect from radiation or chemotherapy.
Sexual arousal is primarily a vasodilation response.
Since the cancer treatments may be drying their system, one may experience arousal changes - they may not feel as much pelvic swelling for women or erectile fullness for men. It's a myth that if you are a cancer survivor, you should just be grateful to be alive. I have heard this voiced by family members, partners and cancer survivors. So I think the biggest, most pernicious myth is that sex is only for people who aren't cancer survivors. A. People need to know they are not alone if they have a question about sex, and they are not alone if they feel that sex is important to them.