People usually ask because they genuinely want to know how you are. Someone that hasn't dealt with cancer or chemo really has no concept of what it's like, so it's quite often simple curiosity and genuine concern. I would expect that the closer someone is to you, the more they want to know. As the daughter and caregiver of a cancer patient, I wanted to know everything about what my dad was going through, not only because I was curious but because I wanted to know if there was something I should or could do to help him. It's hard for people to ask what they can do for you, so they often ask how you are or how chemo went as a way of opening the door for you to let them know if there's something they can do for you. They don't want to appear as though they are pitying you or feeling sorry for you because you have cancer. They just want to be supportive and help in whatever way they can. Let them. Heck, ask if they want to go sit through a chemo treatment with you so they can see what it's about. I'd be willing to bet after they sit there for 3+ hours they'd stop asking how chemo went.
Wishing you all the best in your journey.