Colorectal cancer starts as a small, non-cancerous (benign) lump of cells on the inner lining of the colon or rectum known as a polyp. Some polyps may eventually develop into cancer. Depending on where the cancer begins, it may also be called rectal cancer or colon cancer. Rectal and colon cancers are frequently combined because they share many characteristics. Polyps can be found through screening tests, allowing for their removal before they develop into cancer. Additionally, screening aids in the early detection of colorectal cancer when therapy is most effective.

Symptoms

In the early stages of the disease, colorectal cancer often manifests in many patients without any symptoms. Depending on the size and location of the tumor, different symptoms may present at different times. The following symptoms or indications may be present in patients with colorectal cancer.

• A persistent change in bowel habits, including constipation or diarrhea or a change in stool consistency.

• Tenesmus (perception that the bowels are not emptying).

• Rectal bleeding or bright red or extremely dark blood in the stool.

• Abdomen discomforts include frequent gas pains, bloating, fullness, and cramps.

• Constant weakness or fatigue.

• Unexplained weight loss and/or loss of appetite.

• Anemia due to iron deficiency. 

• Periodic nausea or vomiting without apparent cause.

Diagnosis

The diagnosis of colorectal cancer is made using various tests. When selecting a diagnostic test, several aspects are taken into account, such as the type of cancer suspected, the symptoms, age and general health, medical and family history, and the outcomes of former medical tests. The following tests may be utilized in conjunction with a physical examination to diagnose colorectal cancer.

• Colonoscopy: During a colonoscopy, the clinician can view the complete rectum and colon to check for polyps or other abnormalities. A colonoscopy may occasionally be used to remove colon polyps.

• Biopsy: A biopsy is performed to make an accurate diagnosis of colorectal cancer by removing a small sample of tissue for examination under a microscope. A biopsy can be carried out on tissue that is removed after surgery or during a colonoscopy.

• Biomarker testing: It may be advised to perform laboratory/molecular testing on a tumor to identify genes, proteins, and other characteristics that are particular to the tumor. Testing for mismatch repair defects (dMMRs) is recommended in all colorectal tumors.

• Blood tests: These include a complete blood count (CBC, which helps to detect anemia), liver function tests, and measurement of the levels of carcinoembryonic antigen protein (CEA, as high levels of CEA may signify the spread of cancer).

• Computed tomography (CT) scan and Magnetic resonance imaging (MRI): It can be used to measure the size of the tumor. The progression of cancer to the lungs, liver, and other organs can be monitored using CT and MRI scans.

• Ultrasonography: Endorectal ultrasonography is frequently used to determine how far colorectal cancer has spread and can aid in treatment planning. However, this test is unable to effectively identify cancer that has migrated outside the pelvis or to the surrounding lymph nodes.

• Chest x-ray: If the cancer has metastasized to the lungs, an x-ray of the chest can reveal this.

• Positron emission tomography (PET) or PET-CT scan: F-18 fluorodeoxyglucose (FDG), a mildly radioactive form of sugar that primarily accumulates in cancer cells, is injected into the blood for a PET scan. PET scans are not routinely advised in patients with colorectal cancer. The abdomen, chest, and pelvis are all evaluated during FDG-PET scanning, allowing for the detection of both local and distant metastases. Hepatic and extra-hepatic metastases can both be detected with great sensitivity using FDG-PET. FDG-PET scanning can differentiate between post-treatment (postoperative and post-radiation therapy) scarring and recurrent tumors.

Management

The management strategy of colorectal cancer is decided by the stage and grade of cancer, medical history, and general health of the patients. Treatment options for colorectal cancer may comprise surgery, chemotherapy, immunotherapy, and a combination of various approaches.

Surgery

Surgery is the most common treatment for colorectal cancer. There are different types of surgeries such as:

• Polypectomy: Removal of cancerous polyps.

• Partial colectomy (colon resection surgery): Removal of the tumor-containing portion of the colon, along with some nearby healthy tissue.

• Colostomy: Colostomies are used less frequently to treat rectal or colon cancer patients. This surgical incision, or stoma, connects the colon to the abdominal wall to create an outlet for stool to exit the body. The stool is collected outside the body in a bag. The colon might eventually be reattached, or the stoma might be permanent.

• Radiofrequency ablation: When patients need liver or lung surgery due to metastasis to those organs, radiofrequency ablation is employed. In this procedure, cancer cells are killed using heat. These methods do not work on all liver or lung tumors. This can assist prevent the removal of liver and lung tissue that could otherwise be removed during routine surgery.

Chemotherapy

Chemotherapeutic drugs can kill cancer cells or stop them from proliferating and growing. Chemotherapy is frequently used to treat people with stage 3 or stage 4 colorectal cancer while it may not be necessary for stage 1 or stage 2 colorectal cancer patients. For colorectal cancer, chemotherapy may be neoadjuvant chemotherapy (given prior to surgery) and adjuvant chemotherapy (given after surgery). Chemotherapeutic drugs used in the treatment of colorectal cancer include 5-Fluorouracil (5-FU), Capecitabine (Xeloda), Irinotecan (Camptosar), Oxaliplatin (Eloxatin), Trifluridine and tipiracil (Lonsurf). A combination of 2 to 3 drugs are commonly used to treat colorectal cancer patients.

Radiation Therapy

Radiation therapy is not frequently used to treat colon cancer, although it is more frequently used to treat rectal cancer. For colon cancer, it is used before surgery (combined with chemotherapy, to help shrink a tumor and make it easier to remove), after surgery, or during surgery. However, chemotherapy is frequently administered for rectal cancer either before or after surgery.

Various types of radiation therapy are used to treat colon and rectal cancers which may include external-beam radiation therapy (EBRT), internal radiation therapy (brachytherapy), endocavitary radiation therapy, and interstitial brachytherapy.

Targeted Therapy

Targeted therapy in the treatment of colorectal cancer may include the following drugs:

• Bevacizumab (Avastin)

• Ziv-aflibercept (Zaltrap)

• Ramucirumab (Cyramza)

Every two or three weeks, these drugs are infused into veins (IV), typically in conjunction with chemotherapy.

Immunotherapy

Immunotherapy helps the immune system recognize and eliminate cancer cells more effectively. Some patients with advanced disease may prefer immunotherapy, which includes:

• PD-1 inhibitors: Pembrolizumab (Keytruda) and nivolumab (Opdivo)

• CTLA-4 inhibitor: Ipilimumab (Yervoy). 

Patients with advanced disease are especially recommended to use a combination of these therapies. The incidence and mortality of colorectal cancer are significantly impacted by the early detection of the disease and screening programs.