Final answer:
Colonoscopy with biopsy is indeed the definitive test for diagnosing colorectal cancer, as it allows for the direct visual examination and the potential removal of precancerous polyps, as well as biopsy for cancer confirmation.
Step-by-step explanation:
It is true that colonoscopy with biopsy is the definitive test for the diagnosis of colorectal cancer (CRC). A colonoscopy allows for a direct visual examination of the colon and rectum using a tiny camera at the end of a long tube. This procedure provides the ability to not only detect cancer in its early stages but also to remove precancerous polyps which might develop into cancer. If during a colonoscopy, suspicious areas are identified, a biopsy is performed to confirm the presence of cancer by examining a tissue sample microscopically.
While noninvasive tests like stool DNA tests can indicate the potential presence of cancer cells, they are not definitive. A positive result from such tests necessitates a follow-up with a colonoscopy to visually inspect for cancer or polyps. Therefore, the combination of colonoscopy and biopsy plays a crucial dual role of being both diagnostic and therapeutic in the context of colorectal cancer.