The genealogy of Jesus, whether one of teh major prrofs of Jesus' identity or not (I happen to think that there are much better proofs, such as the resurrection, rather than a Genealogy written several years after his death) does not make any difference as to whether it is part of what is biblically referred to as 'the Gospel'. And it does make just as much sense that we need Jesus without a literal Genesis, do you believe that anyone here is without sin? All have fallen short of the Glory of God, whether this bloke called Adam did it first or not...
Creation, whether literal or not (as I believe that both reveal the important theological truths such as that we all are sinners) is not part of the Gospel. Supportive of the Gospel, certainly, and an explanaton thereof, but it is not par of it in any way. And we are commanded to preach the Gospel, not preach creation. We are commanded to teach each other (christians) about the bible etc, but not non-christians. We can tell them that Jesus came to save us all, and that that is great news. We need to be saved from our own sin, not that of our fathers.
Oh, and its multifactorial genetic instability that causes cancer, not sin. Christians, who are already clean in the eyes of God, still get cancer.
Preach the Gospel of Christ, not of man-made doctrines, whether they are true or not.