It was disappointing for me to see the thread that precipitated this one get so far from OP, it’s one of the things I prayed about yesterday…first to avoid being sucked in and second to remember what really mattered on that thread.
Having experienced the reality of …you have cancer…this is how we plan to treat and btw despite using the most advanced science and tech available, chances are you won’t have children…I’m grateful for the CAF policy of leaving medical advice to those qualified to do so, especially when dealing with moral issues.
Being young and coping with all that cancer brings is a huge burden, I commend the OP for seeking correct Church doctrine on the ancillary medical option of sperm banking…to do so means a great deal with all the other choices, plans and accommodations he must make to support his very real fight ahead.
I didn’t care how hard I’d have to fight to be a mother someday, I held on and fought, many days sicker than a dog it sustained me to hope and dream of what I might be blessed with someday. I’m also grateful my medical situation removed the moral dilemma from me as a choice…the OP docs aren’t talking to him about what a future wife might endure…they are telling him…his options and how far tech has come with great success rates using banked sperm.
My situation placed me near many women enduring IVF/AF processes as I attended my medical needs week after week they spoke openly and vociferously in the waiting rooms.
It sucks to keep finding closed doors that cancer brings…I was fortunate to be in the right place at right time to even have an option of being a mother…it helped to have context that 100 years ago…I’d be dead…what a gift my docs were giving me…being alive to face the road ahead whatever it brought. The OP is beginning a journey most of you never travelled…let his docs be the pros they are.
It’s hard to keep your chin up as docs tell you what they have in their magic bag of tricks, hard to cope with overwhelmed friends who despite good intentions don’t understand what is happening. FYI if someone says, I have leukemia…it’s a blood cancer created in the bone marrow…scalpels may be part of OP future but no scalpel or surgical option cures blood cancers. They have a rough road ahead, no matter how great the meds are at mitigating treatment side effects.
OP asked for Church doctrine for his dilemma but we can’t forget…no Canon law or CCC statement stands alone, in offering the information we are expected to remain in line with our faith of not judging or criticizing someone who seeks the truth. That we have an obligation to remain objective despite fears he might choose sin.
Praying for the docs who offer him the latest and greatest modern medicine has to offer
Praying for the medical support folks who will assist him on the road ahead
Praying for his unmentioned support network…be it family, friends, neighbors etc
Praying for co-workers or fellow students who may be forced to pick up slack to help him along, praying OP will accept help offered and know it’s okay to say…just sit and be present with me…that OP relies on support to give and take the humor ahead! (Personal favorite…imagining wedgies for the kind folks jabbing and poking when it hurts …seems fair to imagine their knickers in a wad

Praying for those he seeks guidance from…that we will remember to be compassionate, empathetic and non judgmental in offering the Churches teaching, respecting his right to free will and encouraging him to establish an ongoing relationship with a local face to face spiritual advisor for the journey ahead.
Praying for everyone who cared enough to reach out to the OP faced with this moral dilemma.