For an FTM it's easier to do the transition (whether before or after, although some surgery options are way beyond normal price options) than an MTF.
Why? I would have thought the reverse. Not to be crude, where does the FTM get the new parts?
Are there issues with cancer since sex hormones are being taken?
Heh.. it's easier to grow hair, go bald, have one's voice drop and remove breasts than the other way. Bottom surgery for an FTM (the creation of a penis) still remains cost-prohibitive (somewhere between $50-100K+ and may or may not work/look like a penis) so many FTMs use a prosthetic of some variation. It's also easier to appear as a short boy or stocky guy.
For an MtF it's harder to remove facial hair (usually requires quite a few electrolysis trips), raise the voice (vocal cord scraping), breast augmentation, etc. Surgeries will total somewhere (I've been told) about $30-40K grand total. Additionally, there have been far more surgeries done for MtFs over the years compared to FTMs (FTM surgery has only been very prominent in the last 10 years or so although there have been some done before this -- it seems in the last 5 years FTM transitioning has picked up as the technology and awareness has gotten better). The actual creation (technical creation) varies from surgeon to surgeon but from what I've understood they'll take a skin graft (from the arm, leg or abdomen) and form the actual penis from that. A tube may be inserted into it to help with urination as well as addition options to give it the effect of "erection".
As for cancer and other health risks, there are always risks. Any doctor will do proper blood work before and during hormone treatment. Using myself as an example, I have to watch out not only for my female born risks (until I have a hysto -- a common procedure for an FTM -- I still run the risk of ovarian cancer) but I also have to watch out for baldness (oh yay.
), high cholesterol and other male issues (prostate cancer isn't a risk AFAIK
Hopefully that answers your question. As an FYI: I'm pretty open about my own transition but others may not be so others who transition might find your question a little putting off.