Rectal Cancer: Causes, Symptoms, Diagnosis and Treatment — Overview, Diagnosis & Treatment Options | MyMedicPlus

Rectal cancer arises in the rectum — the final 12-15 cm of the large intestine — and accounts for approximately 28-30% of all colorectal cancers. Approximately 46,000 new cases are diagnosed annually in the United States, making it one of the most common gastrointestinal malignancies. The anatomical constraints of the pelvis — proximity to the urinary bladder, prostate or uterus, pelvic nerves, and anal sphincter — make rectal cancer fundamentally distinct from colon cancer in surgical approach and radiation planning. Total mesorectal excision (TME), a specialized surgical technique, and multimodality neoadjuvant therapy are essential components of care. The disease is predominantly rectal adenocarcinoma; rectal carcinoid and squamous carcinoma (of the anal margin) are distinct entities with different management. Increasing incidence of rectal cancer in adults under age 50 has been noted in developed nations and represents a growing clinical challenge for which established screening thresholds (typically starting at 45-50 years) may need reconsideration.

Colorectal cancer risk factors apply to rectal cancer: a Western diet high in processed red meat and low in dietary fiber; sedentary lifestyle and obesity; tobacco smoking; and heavy alcohol consumption each contribute incrementally. Hereditary syndromes account for approximately 5-10% of rectal cancer: Lynch syndrome (germline mutations in MLH1, MSH2, MSH6, and PMS2 mismatch repair genes) confers approximately 40-70% lifetime colorectal cancer risk and is detectable by MSI or mismatch repair protein IHC testing of all colorectal cancers (universal screening is recommended). Familial adenomatous polyposis (FAP, germline APC mutation) leads to hundreds to thousands of colorectal polyps and near-certain colorectal cancer without prophylactic colectomy. MUTYH-associated polyposis (MAP, MUTYH biallelic mutations) is a recessive polyposis syndrome. Inflammatory bowel disease — particularly longstanding ulcerative colitis and Crohn's colitis — substantially increases colorectal cancer risk proportional to duration, extent, and severity of inflammation. Prior pelvic irradiation and diabetes mellitus are additional risk factors.

Rectal cancer produces locally specific symptoms reflecting its anatomical location in the terminal bowel and pelvis. Rectal bleeding — visible bright red blood mixed with or coating the stool — is the most common and important symptom, present in approximately 60-90% of patients. This is often initially attributed to hemorrhoids, causing dangerous diagnostic delay, particularly in younger adults. Change in bowel habits is characteristic: alternating constipation and diarrhea, tenesmus (the persistent and distressing feeling of incomplete bowel evacuation), and passage of increasingly narrow or pencil-thin stools reflecting circumferential tumor growth. Mucus discharge from the rectum is common with low-lying tumors. Pelvic or perirectal pain is a late symptom suggesting perirectal tissue invasion. Advanced disease may cause urinary symptoms from bladder or ureter invasion, vaginal symptoms, or sciatic nerve pain from sacral invasion. Obstruction (complete inability to pass stool, abdominal distension) and perforation are emergency presentations. Many cases in organized screening programs are detected at asymptomatic Stage I.

Colonoscopy with biopsy of the rectal mass is the primary diagnostic procedure; synchronous colon lesions (present in approximately 3-5%) are identified at the same time. High-resolution MRI of the pelvis (3 mm slice thickness, phased-array coil) is the gold standard for local staging: it characterizes T stage (tumor penetration through the rectal wall layers), N stage (mesorectal and lateral pelvic lymph node involvement), the circumferential resection margin (CRM), and the distance to the anal sphincter complex — all critical for surgical and oncological planning. Endorectal ultrasound provides complementary T staging for early lesions (T1-T2). CT of the chest and abdomen/pelvis detects hepatic and pulmonary metastases. Molecular profiling of all rectal cancers is standard: MSI/dMMR testing (universal Lynch syndrome screening), KRAS/NRAS/BRAF V600E (predicts anti-EGFR antibody benefit in metastatic disease), ERBB2/HER2 amplification, and RAS/RAF wild-type status. TNM staging (AJCC 8th edition).

Total neoadjuvant therapy (TNT) — delivering all systemic and radiation therapy before surgery — has become the standard approach for stage II-III rectal cancer, based on the RAPIDO and PRODIGE 23 trials demonstrating higher pathological complete response (pCR) rates and organ preservation compared to chemoradiation alone. The TNT approach most commonly consists of induction FOLFOX or CAPOX chemotherapy (4-6 cycles) followed by long-course chemoradiation (capecitabine or infusional 5-FU plus 50.4 Gy in 28 fractions), or alternatively short-course radiotherapy (5 Gy x 5 fractions) followed by consolidation FOLFOX chemotherapy (RAPIDO trial). After TNT, total mesorectal excision (TME) — performed laparoscopically, robotically, or open — is standard. For patients who achieve clinical complete response (cCR) to TNT, organ preservation with intensive watch-and-wait surveillance (MRI, endoscopy, CEA every 3 months for 2 years) avoids permanent colostomy in selected patients (OPRA trial: approximately 40% achieve durable organ preservation at 3 years). For dMMR/MSI-H rectal cancer, neoadjuvant pembrolizumab alone (without chemotherapy or radiation) achieved pCR in approximately 60% of patients in a pivotal Memorial Sloan Kettering trial, with some patients avoiding surgery entirely — a practice-changing finding. For metastatic rectal cancer, FOLFOX, FOLFIRI, or FOLFOXIRI combined with bevacizumab or anti-EGFR antibodies (cetuximab, panitumumab for RAS/BRAF wild-type), plus pembrolizumab for dMMR, are the systemic options.

Colorectal cancer screening beginning at age 45 for average-risk individuals — with colonoscopy every 10 years, or annual high-sensitivity fecal occult blood testing (FIT), or flexible sigmoidoscopy every 5 years with annual FIT, or CT colonography every 5 years — is the most effective prevention strategy. Colonoscopic polypectomy of adenomatous polyps prevents colorectal cancer by removing precursor lesions; patients with advanced adenomas require shorter surveillance intervals. High-risk individuals begin screening earlier: age 20-25 for Lynch syndrome carriers; age 10-15 for FAP; 10 years before the youngest affected first-degree relative for those with a strong family history. Lifestyle modifications — maintaining a healthy BMI, engaging in regular physical activity, eating a diet rich in vegetables and whole grains and limiting processed red meat and alcohol — have established evidence for colorectal cancer risk reduction. Daily aspirin use reduces colorectal cancer risk in clinical trials but is not recommended solely for this indication without cardiovascular risk-benefit assessment.

Rectal bleeding — any blood in or around the stool, on toilet paper, or in the toilet bowl — should be medically evaluated within 2-4 weeks if not clearly explained by a known benign cause such as hemorrhoids. Critically, attributing rectal bleeding to hemorrhoids without colonoscopic examination in a patient over 40 or with any change in bowel habits is a well-recognized cause of delayed rectal cancer diagnosis. Tenesmus (persistent feeling of incomplete evacuation), a notable change in stool caliber or frequency lasting more than 2 weeks, or unexplained pelvic pain in a patient over 45 requires colonoscopy referral. Adults under 50 with rectal bleeding or unexplained bowel habit changes should also be evaluated promptly rather than reassured based on age alone, given the increasing incidence of early-onset colorectal cancer. Any first-degree relative of a Lynch syndrome patient should be offered genetic counseling and colonoscopy starting at age 20-25 or 10 years before the youngest affected relative.

Stage I: 5-year survival approximately 90%. Stage II: approximately 75-80%. Stage III: approximately 55-70% (improving with TNT and intensified chemotherapy). Stage IV: approximately 15-20%. dMMR/MSI-H rectal cancers achieve clinical complete response in approximately 60% with pembrolizumab, with many patients potentially avoiding surgery. MSS rectal cancer has limited immunotherapy benefit outside of dMMR context. The prognosis for Rectal Cancer: Causes, Symptoms, Diagnosis and Treatment varies depending on severity at diagnosis, the patient's overall health, and how promptly treatment is initiated. With early diagnosis and appropriate management, many patients achieve good outcomes and maintain quality of life. Regular follow-up with healthcare providers is essential to monitor progress, adjust treatment as needed, and detect any complications early. Adherence to prescribed treatments and lifestyle modifications significantly improves long-term prognosis.