This topic is a bit old but i stumbled uppon it and figurred i'd have a go at sharring my knowledge in the area while i'm here.
I finnished a bachelor of science recently (i studied biomedical science: so a fair bit of anatomy, physiology, immunology, cell biology, microbiology... all kinda useful here). I also did a madly excessive amount of reading before i got the vaccine.
There's a fair bit of miss-information out there about who needs a pap, even among doctors. A lot of doctors don't even know that lesbians need pap smears so i doubt their ability to advise transmen unless they work at a gender clinic... and even then i'm not sure.
I think it is theoretically possible for almost any body part to spontaniously turn cancerous if you're unlucky enough, but the vast majority of cervical cancers (what the pap is looking for) are caused by a virus called HPV.
HPV is spread by sexual contact so if you have never had sexual contact with anyone (male or female) under normal circumstances you probably wouldn't need a pap. But transitioning probably isn't really "normal" circumstances.
I know intersex people, and people with hormonal imbalances, tend to be at a much higher risk of developing cancers in their sexual organs. I must admit i don't know if this applies to people who are transitioning under conttrolled circumstances though. I know Candy Darling (an M2F from the 1970ish) died of cancer related to her hormones, but i'll confess a lack of knowledge there. If your doctor thinks you still need a pap even though you are a virgin because you are on T, or on an unusual pill to stop periods, it's probably worth the embarrassmet just in case.
But i imagine that would be very few of you. I think the mechinism of transmission of HPV is a bit unclear. It used to be thought you could only catch it from a man, but they now think it can be transmitted between women. Pap smears are now recomended for lesbians under the same rules as straight women, i.e. after the onset of sexual activity.
If you have never had sex involving vaginal penetration at all, but have had some sexual contact with a man or woman (e.g. anal or clitoral). I don't think even the world experts on the virus could tell you if you were at risk. The risk is probably smaller than that for someone who has engaged in penetrative vaginal sex (be it penis, toys, or fingers), but it is probably still a big enough risk to make pap smears worth while, particularly if you are also stressing your female organs by taking hormones for transition.
As for pain, all i can say is relax. Biting down on a towel and tensing up is probably counter-productive? None of my female friends have told me about anything more than "discomfort" durring a pap. Also, tell the doctor clearly if it hurts, they may be able to do something to prevent it.