[highclass]

Finger check will usually only detect a huge prostate or rectal cancer(not other portions of the colon), or a rectal cancer just next to the anal canal.

Colonoscopy(can detect polyps BEFORE they become cancer, but more costly and hard for patient) is the gold standard for detecting colon cancer, along with fecal occult blood which is cheap and easier to do but will detect only more advanced cancers. For prostate, the early detection and screening is usually using done using a PSA blood test.

[Engineering-MD]

You can actually detect relatively small prostate cancers, even more so for superficial ones. PSA is not raised in all prostate cancers and cannot be used with prostate examination to rule out prostate cancer.

[Engineering-MD]

Should read: Cannot be used ^without prostate examination