Rectal Cancer

Background:

• Rectal cancer is a subtype of colorectal cancer, but clinically behaves differently from colon cancer (its pelvic location creates unique challenges related to local recurrence, resection margins, sphincter preservation, and radiation planning)

• Accounts for ~40% of all colorectal cancers

• Most rectal cancers are adenocarcinoma

• Key risk factors overlap with colorectal cancer:

  • Age, prior adenomas/CRC, family history, Lynch syndrome/FAP, IBD, obesity, smoking, alcohol, diet high in red/processed meat, low physical activity.

• The rectum extends from the rectosigmoid junction to the anal canal and is approximately 15 cm long. Clinically, rectal tumors are categorized based on the distance of the tumor from anal verge:

  • 0 - 5 cm from anal verge: Low rectal cancer

    • More likely to involve the sphincter complex and levator muscles, making sphincter preservation more challenging.

  • >5 - 10 cm from anal verge: Mid rectal cancer

    • Often amenable to sphincter-preserving surgery depending on response to neoadjuvant therapy and tumor extent.

  • >10 - 15 cm from anal verge: High rectal cancer

    • Behave more like colon tumors and may lie above the peritoneal reflection.

• Lymphatic drainage of rectum:

  • Proximal rectal tumors:

    • often drain upward through the mesorectal/superior rectal pathway.

  • Distal rectal tumors:

    • likely have both upward and lateral lymphatic drainage, which affects surgical/radiation planning.

  • Very low rectal tumors (extended into the anal canal below the dentate line):

    • may involve the inguinal lymph nodes (require consideration of inguinal nodal evaluation and/or treatment)

    
    

Work-up:

• CBC, CMP, CEA

• Colonoscopy with biopsy

• Pelvic MRI

  • Gold standard for local staging

  • Also reports circumferential resection margin (CRM), extramural vascular invasion (EMVI), and mesorectal fascia involvement, which strongly influence treatment decisions.

• Endorectal ultrasound

  • if MRI is contraindicated

  • if lesion is superficial

• Universal MMR/MSI testing on all newly diagnosed rectal cancers

• Testing for somatic PI3K pathway alterations (stage II–III)

• Chest/abdomen CT or MRI

• PET scan is NOT indicated for non-metastatic disease

• If metastatic disease:

  • Requires additional biomarker testing including KRAS, NRAS, BRAF V600E, HER2 (ERBB2) overexpression/amplification, MMR/MSI status

Staging:

• T stage:

  • T1: Invades submucosa

  • T2: Invades muscularis propria

  • T3: Invades perirectal tissues

  • T4: Invades visceral peritoneum or adjacent organs

• N stage:

  • N1: 1–3 positive regional LN

    • N1c: No positive LN but tumor deposits are present in the perirectal tissues

  • N2: ≥4 positive regional LN

• M stage:

  • M1a: Metastasis to 1 distant site (No peritoneal metastasis)

  • M1b: Metastasis to ≥2 distant sites (No peritoneal metastasis)

  • M1c: Peritoneal metastasis (± other organ metastases)

IN PROGRESS...