Rectal Cancer

The rectum is the final part of the large intestine, connecting the sigmoid colon to the anal canal.

Although rectal and colon cancers are both colorectal cancers, rectal cancer is managed somewhat differently because the rectum lies deep within the pelvis close to structures such as the bladder, prostate, vagina, sacrum, and pelvic nerves.

Most rectal cancers are adenocarcinomas.

Modern treatment planning considers not only TNM stage but also pelvic MRI findings, including the relationship of the tumor to the mesorectal fascia, extramural vascular invasion, lymph nodes, and the distance between the tumor and the anal sphincter.

Rectal cancer usually develops through a combination of genetic, age-related, lifestyle, and medical factors rather than from a single cause.

Risk factors for colorectal cancer include increasing age, a personal or family history of colorectal cancer or adenomatous polyps, inflammatory bowel disease, inherited syndromes such as Lynch syndrome and familial adenomatous polyposis, smoking, heavy alcohol use, obesity, physical inactivity, certain dietary patterns, and type 2 diabetes.

Early rectal cancer may cause no noticeable symptoms.

Possible signs and symptoms include rectal bleeding, changes in bowel habits, more frequent bowel movements, a feeling of incomplete evacuation, narrowing of the stool, mucus in the stool, abdominal pain or bloating, constipation or diarrhea, unexplained weight loss, fatigue, or anemia.

Rectal bleeding can sometimes be mistaken for hemorrhoids, but the cause cannot be determined reliably from the appearance of the blood alone. Persistent or recurrent bleeding should be medically evaluated.

More advanced local disease may cause bowel obstruction, urinary symptoms, abnormal vaginal discharge, or pelvic and sacral pain.

Diagnosis typically includes endoscopy, tissue biopsy, and imaging for staging.

Colonoscopy is an important diagnostic test because it allows direct examination of the rectum and the rest of the colon and enables biopsy of suspicious lesions.

After diagnosis, pelvic MRI is one of the key tests for local staging. It helps assess the depth of tumor invasion, mesorectal lymph nodes, the mesorectal fascia, and nearby pelvic structures.

CT of the chest, abdomen, and pelvis is commonly used to evaluate distant spread, particularly to the liver and lungs.

Endorectal ultrasound may be useful for selected very early tumors.

PET/CT is not routinely required for every newly diagnosed patient and is generally reserved for selected situations.

CEA can support follow-up and treatment monitoring but cannot diagnose rectal cancer by itself.

Testing for mismatch repair deficiency or microsatellite instability is also important because it can affect hereditary cancer evaluation and treatment decisions.

Staging and Local Risk Assessment

Rectal cancer is primarily staged using the AJCC TNM system.

T describes the depth and local extent of the primary tumor, N describes regional lymph node involvement, and M indicates distant metastases.

However, stage alone does not fully determine treatment. Pelvic MRI findings such as mesorectal fascia involvement, extramural vascular invasion, tumor height, and lymph node characteristics can also influence the treatment strategy.

Treatment for rectal cancer should be jointly developed by a multidisciplinary team including colorectal surgery, medical oncology, radiation oncology, radiology, and pathology, based on tumor stage, location, high-risk factors on pelvic MRI, MMR/MSI status, and the patient’s overall condition.

Modern rectal cancer treatment is no longer simply “chemoradiotherapy first, then surgery, then chemotherapy.” The treatment sequence can differ markedly among patients with different risk profiles.

Early Rectal Cancer

Selected very early rectal cancers with favorable features may be treated with local excision rather than radical rectal surgery.

Local procedures can be performed through the anus and may preserve rectal and sphincter function.

Because local excision does not remove regional lymph nodes, careful patient selection is essential. Additional treatment may be recommended if pathology reveals higher-risk features.

Locally Advanced Rectal Cancer (LARC) and Total Neoadjuvant Therapy (TNT)

For many patients with stage II or III rectal cancer or other high-risk local features, total neoadjuvant therapy (TNT) is now an important treatment strategy.

TNT delivers chemotherapy and radiation-based treatment before surgery rather than splitting systemic therapy between the preoperative and postoperative periods.

Treatment may involve chemotherapy followed by chemoradiation or chemoradiation followed by consolidation chemotherapy.

After treatment, the tumor is reassessed and surgery—typically total mesorectal excision—is considered.

NCI currently describes TNT as a preferred approach for most patients with locally advanced, nonmetastatic rectal cancer.

Total mesorectal excision (TME)

Total mesorectal excision (TME) is a fundamental surgical principle for many mid- and low-rectal cancers.

The operation depends on tumor location, sphincter involvement, surrounding structures, and functional considerations.

Low anterior resection or other sphincter-preserving procedures may be possible when adequate cancer margins can be achieved while preserving useful sphincter function.

If the sphincter is involved or adequate margins cannot be achieved safely, abdominoperineal resection with a permanent colostomy may be necessary.

A fixed distance from the anal sphincter does not by itself determine whether sphincter preservation is possible.

Immunotherapy for dMMR/MSI-H Rectal Cancer

Immunotherapy is one of the most important recent developments in rectal cancer treatment.

A minority of rectal adenocarcinomas are mismatch repair deficient (dMMR) or microsatellite instability-high (MSI-H). These tumors can be particularly sensitive to PD-1 checkpoint inhibition.

In locally advanced dMMR rectal cancer, studies of neoadjuvant dostarlimab have shown striking clinical complete responses, allowing some patients to avoid chemoradiation and surgery.

This field is evolving rapidly, and decisions about immunotherapy alone or omission of surgery should be made by experienced multidisciplinary teams according to current evidence and local approvals.

Metastatic Rectal Cancer

Metastatic rectal cancer is not treated with chemotherapy alone in every case.

The first question is whether distant metastases—particularly in the liver or lungs—can be completely removed or potentially converted to resectability after systemic treatment.

Selected patients with limited resectable metastases may still receive treatment with curative intent, including surgery or local ablation together with systemic therapy.

For unresectable metastatic disease, systemic therapy is the main approach. Treatment may include fluoropyrimidine-based chemotherapy combined with oxaliplatin or irinotecan and targeted or immune therapies selected according to biomarkers such as RAS, BRAF, HER2, and MMR/MSI status.