Rectal Cancer
Rectal cancer is a cancer arising in the rectum, the final portion of the large intestine that connects the sigmoid colon to the anus. Although rectal cancer shares many features with colon cancer—both are usually adenocarcinomas that develop from precancerous polyps—it has important differences in evaluation, staging, and treatment. The rectum’s location deep in the pelvis, close to critical structures such as the anal sphincter, sexual organs, and pelvic nerves, makes rectal cancer treatment particularly complex. Modern management typically involves careful staging with pelvic MRI, multimodal treatment combining chemotherapy, radiation, and surgery, and, increasingly, bladder- and sphincter-sparing approaches. Effective treatment often requires coordinated care by an experienced multidisciplinary team.
What is it?
The rectum is the final portion of the large intestine, typically about 12 to 15 centimeters long, that connects the sigmoid colon to the anal canal. It is located deep in the pelvis and is surrounded by structures that are important both for daily function and for cancer treatment planning: the anal sphincter (which controls bowel continence), the bladder, prostate, and seminal vesicles in men, the uterus, vagina, and ovaries in women, and important pelvic nerves that control urinary, sexual, and bowel function. The rectum is surrounded by a fatty tissue layer called the mesorectum, which contains blood vessels, lymphatics, and lymph nodes; the mesorectum is enclosed by a thin layer of tissue called the mesorectal fascia.
Rectal cancer arises from cells in the rectal wall. The vast majority (over 95%) of rectal cancers are adenocarcinomas, which develop from the glandular cells lining the inner surface of the rectum. Other, less common types include squamous cell carcinoma (more common in the anal canal but occasionally in the rectum), neuroendocrine tumors (carcinoids), lymphomas, gastrointestinal stromal tumors (GISTs), and metastases from other cancers—these are discussed on separate pages.
Rectal cancer typically develops slowly, over 10 or more years in most cases, from precancerous polyps through the adenoma-carcinoma sequence. Most rectal cancers arise from adenomatous polyps, particularly certain types such as tubular, tubulovillous, and villous adenomas. As in the colon, this slow, stepwise progression makes screening highly effective at both preventing cancer (through removal of precancerous polyps) and detecting it early.
Rectal cancer shares many risk factors with colon cancer, including advancing age, family history, inherited syndromes (Lynch syndrome, familial adenomatous polyposis, and others), a personal history of colorectal polyps or cancer, inflammatory bowel disease (particularly ulcerative colitis with extensive involvement), lifestyle factors (obesity, physical inactivity, high consumption of red and processed meats, low fiber intake, heavy alcohol use, smoking), and type 2 diabetes. Rates of early-onset colorectal cancer (in adults under 50) have been increasing, and this has prompted lowering of the recommended screening age. Rectal cancer is slightly more common in men than women.
The rectum’s location deep in the pelvis creates several important differences from colon cancer:
The rectum is surrounded by other important structures that can be involved in local tumor spread or affected by treatment. This makes local (pelvic) control of the tumor critically important.
The lymphatic drainage of the rectum is different from that of the colon, with lower rectal tumors potentially spreading to different lymph node groups than upper rectal tumors.
The tumor’s distance from the anal sphincter significantly affects whether sphincter-preserving surgery is possible.
Radiation therapy is more commonly used for rectal cancer than for colon cancer, in part because the rectum’s location in the pelvis allows for targeted radiation and in part because local recurrence is a particular concern with rectal cancer.
The surgical approach is different, and preservation of pelvic nerves that control urinary, sexual, and bowel function is a particular consideration in rectal cancer surgery.
Symptoms of rectal cancer depend on the location, size, and stage of the tumor. Common symptoms include bleeding from the rectum (which is often visible red blood, sometimes mixed with stool or coating the surface of the stool, and is one of the most common presenting symptoms), change in bowel habits (constipation, diarrhea, or alternating patterns), change in stool caliber (thinner stools), sensation of incomplete emptying after bowel movements (tenesmus), pelvic or rectal pain (typically in more advanced disease), unintended weight loss, and fatigue (often from anemia due to bleeding). In advanced cases, symptoms may include severe pelvic pain, urinary symptoms (from local invasion into the bladder), fistula formation (abnormal connections between the rectum and other pelvic organs such as the vagina), or symptoms related to distant spread.
Because rectal bleeding is common in the general population from benign causes such as hemorrhoids or anal fissures, and because early rectal cancer symptoms can be nonspecific, there is often a delay between symptom onset and diagnosis. Any unexplained rectal bleeding in an adult, particularly if new or persistent, warrants evaluation. Early cancers often cause few or no symptoms, which is why screening is so highly recommended.
Diagnosis of rectal cancer typically involves several components.
Digital rectal examination (a physical examination in which a gloved finger is inserted into the rectum) is important for evaluating lower rectal tumors and provides information about the tumor’s location, size, mobility, and relationship to the anal sphincter. Many lower rectal tumors can be palpated on examination.
Endoscopy is essential for diagnosis. Colonoscopy examines the entire colon and rectum and allows biopsy of the tumor. Flexible sigmoidoscopy is an alternative that examines the rectum and lower colon but does not evaluate the more proximal colon. Colonoscopy is generally preferred because it also identifies any additional lesions or polyps that require attention.
Once rectal cancer is diagnosed by biopsy, careful staging is essential and involves multiple components.
Local staging evaluates the tumor’s depth of invasion into the rectal wall, extension into or beyond the mesorectal fascia, and involvement of nearby lymph nodes. Pelvic MRI is the gold standard for local staging and provides detailed information about the tumor’s relationship to the mesorectal fascia (the “circumferential resection margin,” or CRM, which is critical for surgical planning), the anal sphincter, and other pelvic structures. MRI also identifies lymph nodes that appear enlarged or otherwise concerning. Endorectal ultrasound (EUS) is an alternative approach that can provide detailed information about the depth of invasion, particularly for early tumors, and is used in some centers. Standardized MRI reporting frameworks and templates help ensure comprehensive evaluation.
Distant staging evaluates for spread beyond the pelvis. CT of the chest, abdomen, and pelvis is the primary test for distant staging and evaluates for lung and liver metastases in particular. PET/CT is used in specific circumstances, particularly for equivocal findings on CT or in planning treatment of oligometastatic disease.
Blood tests include complete blood count, kidney and liver function tests, and tumor markers such as CEA (carcinoembryonic antigen). CEA can be elevated in rectal cancer and useful for monitoring during and after treatment, though it is not specific.
Molecular testing of the tumor is increasingly important and guides treatment decisions. Testing typically includes mismatch repair (MMR) protein status or microsatellite instability (MSI) status, RAS mutations (KRAS, NRAS), BRAF mutations, HER2 status, and other markers depending on the specific circumstances.
For patients with suspected hereditary syndromes (based on young age at diagnosis, family history, multiple primary cancers, or specific tumor features), evaluation may include genetic counseling and germline genetic testing.
Rectal cancer staging uses the TNM (tumor, node, metastasis) system, similar to colon cancer, but the specific implications for treatment planning include the tumor’s exact location within the rectum, its relationship to the anal sphincter, and its relationship to the mesorectal fascia.
Important to Know
Management of rectal cancer is highly individualized and typically involves a multimodal approach combining surgery, chemotherapy, and, for many patients, radiation therapy. Care is best delivered by multidisciplinary teams at centers with significant experience in rectal cancer, including colorectal surgeons, medical oncologists, radiation oncologists, radiologists with expertise in pelvic MRI, pathologists, gastroenterologists, and, when needed, other specialists including plastic surgeons, urologists, and gynecologic surgeons.
For very early rectal cancers (particularly those confined to a polyp with favorable features), endoscopic resection or local excision may be appropriate in selected cases with careful pathologic evaluation and follow-up.
For localized rectal cancer that is more than very superficial, treatment approach depends on the stage, tumor location, and specific features.
For low-risk stage I to select low-risk stage II tumors that are away from the anal sphincter, surgery alone may be appropriate. Total mesorectal excision (TME)—which involves removal of the rectum along with the mesorectum enclosed by the mesorectal fascia—is the standard surgical technique and has significantly improved outcomes since its introduction. TME can be performed as a sphincter-preserving procedure (low anterior resection, or LAR) when the tumor is above the anal sphincter with adequate distance from it. LAR allows reconnection of the colon to the remaining lower rectum or, in very low tumors, to the anal canal, preserving natural continence in many patients. For very low tumors that involve the anal sphincter or are very close to it, abdominoperineal resection (APR)—which involves removal of the rectum along with the anal sphincter—is often necessary, and this procedure requires a permanent colostomy (an opening in the abdominal wall through which stool is diverted into a bag).
For locally advanced rectal cancer (larger tumors, those with concerning lymph node involvement on imaging, or those with features suggesting risk of local recurrence), multimodal treatment with a combination of surgery, chemotherapy, and radiation is standard. Historically, this typically involved neoadjuvant chemoradiation (chemotherapy and radiation together before surgery) followed by surgery and then adjuvant chemotherapy after surgery. More recently, total neoadjuvant therapy (TNT)—which delivers all chemotherapy and radiation before surgery—has become increasingly used based on results from trials such as PRODIGE 23, RAPIDO, and OPRA. TNT approaches have shown advantages in terms of pathologic complete response rates, treatment completion rates, and, in some studies, disease-free survival.
Watch-and-wait (nonoperative management) is an emerging option for selected patients who achieve a complete clinical response after neoadjuvant therapy. Rather than proceeding to surgery when no evidence of residual cancer is identified after treatment, patients are followed with close surveillance (regular endoscopy, MRI, and clinical assessment). This approach can preserve the rectum and avoid the potential complications and quality-of-life impact of surgery. Approximately one-third or more of patients with locally advanced rectal cancer treated with TNT may achieve a complete clinical response and be eligible for watch-and-wait in specialized centers. However, a proportion of these patients will develop tumor regrowth and require salvage surgery, so ongoing intensive surveillance is essential. Watch-and-wait requires care at experienced centers with the multidisciplinary expertise for careful patient selection and follow-up.
For MMR-deficient (MMRd) or microsatellite instability-high (MSI-H) rectal cancer, immunotherapy has emerged as a highly effective treatment option. Recent trials (such as the study by Cercek and colleagues at Memorial Sloan Kettering) have shown that neoadjuvant immunotherapy alone can achieve remarkable complete response rates in MMRd rectal cancer, potentially avoiding both chemotherapy/radiation and surgery in many patients. MMRd/MSI-H tumors represent a small subset of rectal cancers (approximately 5% or so) but are particularly important to identify because of these transformative treatment options.
For metastatic (stage IV) rectal cancer, treatment approaches parallel those for metastatic colon cancer and include systemic chemotherapy (with fluoropyrimidines, oxaliplatin, and/or irinotecan in various combinations), targeted therapies matched to molecular characteristics (EGFR-directed therapies in RAS wild-type tumors, VEGF-directed therapies, BRAF-directed therapies for BRAF V600E-mutant tumors, HER2-directed therapies, and others), immunotherapy for MMRd/MSI-H tumors, and, in selected patients with limited metastatic disease, surgical resection of metastases or other local treatments such as thermal ablation or stereotactic body radiation therapy (SBRT).
Radiation therapy for rectal cancer is typically delivered as external beam radiation over several weeks (typically about 5–6 weeks) or, in some approaches (particularly with RAPIDO-style TNT), as short-course radiation delivered over 5 days followed by chemotherapy. Radiation planning uses advanced techniques to focus radiation on the tumor while minimizing exposure to surrounding structures such as the small bowel, bladder, and reproductive organs.
Surgical considerations for rectal cancer are complex. Sphincter preservation is a major goal when feasible. Nerve preservation (of the autonomic nerves that control urinary, sexual, and bowel function) is important, and total mesorectal excision performed by experienced surgeons is designed to preserve these nerves when possible. For patients undergoing LAR, a temporary diverting ileostomy (an opening in the abdominal wall through which stool is diverted from the small intestine) is often created to allow the surgical connection to heal, and is typically reversed a few months later. For patients undergoing APR, a permanent colostomy is required, and specialized support and education for stoma care are essential.
Following surgery, additional (adjuvant) chemotherapy may be given if not fully delivered before surgery. For patients treated with TNT, the balance of chemotherapy and radiation may have been completed before surgery, and further systemic treatment may not be needed.
For patients with confirmed or suspected Lynch syndrome, coordinated care includes treatment of the current cancer, genetic counseling, family screening, and long-term surveillance for other Lynch-associated cancers.
Recovery after rectal cancer surgery can be challenging, and long-term effects can include changes in bowel function (such as increased frequency, urgency, and clustering of bowel movements, sometimes called “low anterior resection syndrome”), urinary and sexual dysfunction (from effects on pelvic nerves), and, for patients with a permanent stoma, adjustment to stoma care and its impact on daily life. Multidisciplinary support—including specialized stoma nursing, physical therapy, pelvic floor rehabilitation, sexual health support, and mental health support—is important and can significantly improve quality of life.
Long-term follow-up is essential because of the risk of recurrence. Standard surveillance typically includes clinical assessment, CEA levels, CT imaging, colonoscopy at defined intervals, and, in patients treated with watch-and-wait, more intensive rectal-specific surveillance with MRI and endoscopy. Surveillance schedules are individualized based on stage, treatment, and other factors.
For patients considering fertility preservation before treatment, coordination with reproductive medicine is important, particularly before pelvic radiation.
Care during pregnancy in patients with rectal cancer is highly complex and requires coordination among oncology, obstetrics, maternal-fetal medicine, surgery, and, when relevant, radiation oncology. Treatment decisions balance the mother’s oncologic needs with fetal safety.
Nutritional support, mental health support, and support for family and caregivers are important components of comprehensive care.
For patients with advanced disease, palliative care is an important component of treatment and can be integrated alongside cancer-directed therapy at any stage.
Care is best coordinated by multidisciplinary teams at high-volume rectal cancer centers when available. Imaging, laboratory, pathology, and molecular findings are interpreted alongside the patient’s symptoms, examination, family history, and broader clinical context rather than in isolation.
Patient education plays an essential role. Understanding the diagnosis, the specific characteristics of the tumor including molecular features, the rationale for the recommended treatment plan (including the increasing use of TNT and watch-and-wait in appropriate patients), the potential effects of treatment on bowel, urinary, and sexual function, the significance of hereditary syndromes when identified, and warning signs of complications or recurrence all contribute to better outcomes. Shared decision-making is particularly important given the complexity of treatment options and their potential impact on quality of life.
Red flag symptoms include severe abdominal or pelvic pain, symptoms of bowel obstruction (severe abdominal pain, distention, vomiting, inability to pass stool or gas), significant gastrointestinal bleeding (large amounts of visible blood, black tarry stools, or lightheadedness with bleeding), high fever with signs of severe infection, sudden severe pain (which may suggest perforation), signs of sepsis, sudden inability to urinate or new severe pelvic pain (which may suggest local invasion or obstruction), difficulty breathing (which may suggest lung metastases), new severe back pain with weakness, numbness, or bowel or bladder changes (which may indicate spinal cord compression from metastases), unintended significant weight loss, or rapid clinical deterioration. These warrant prompt or urgent medical evaluation.