cancers are either carcinomas or sarcomas.. then the sudividisions come.

Most cancers can fit in one of four broad groups:
Carcinoma, sarcoma, leukemia, lymphoma. Melanoma and some brain tumors do not play nicely with those groups, however.

Adenomas are benign gland-forming tumors. Adenocarcinoma is a specific subtype of carcinoma.

Carcinomas arise from epithelial tissues, and comprise by far the bulk of malignancies.

Why epithelial tissue gets picked on- my thoughts:
1) volume/ # of cells at risk (just more of them)
2) More active? ie., cell division, particularly as compared with neural tissue
3) More differentiation to create the various organs, which increases the complexity, and makes genetic mistakes seemingly more likely
4) Also, since skin cancers comprise many of the carcinomas, this is also an exposure issue (like sun), also lung cancer an example here (smoking).

Numerically, over 90% of all cancers are skin cancers.

You can look up your own answers to your cancer statistics questions here.

http://www.cancer.org/docroot/stt/stt_0.asp