Antibodies recognizing TAG-72 provide a novel approach for the imaging, detection, and treatment of cancer. These methods are made possible by using antibody fragments that bind specifically to the sialyl-Tn surface adhesin of TAG-72. Antibody fragment derivatives are advantageously useful over other antibody and antibody fragments known in the art because they are easy to express in large quantities, can penetrate tissues easily and lack the constant domains that promote often unwanted and usually superfluous effector functions.