Ca Rectum Basics Flashcards
(14 cards)
Familial colorectal cancer syndrome
- FAP -
AD; APC gene mutation on chromosome 5; variants are-
a. Gardener’s (sarcomas, osteomas, desmoid tumors)
b. Turcot’s (GBM, medulloblastoma) - HNPCC (Lynch syndrome) -
mismatch repair gene mutation (hMLH1, hMSH2/6 or PMS2) - leads to mictosatellite instability
Increased risk of endometrial. ovarian, stomach, small bowel etc
Rectum extent
Rectum is ~12 to 15 cm in length, beginning proximally at rectosigmoid junction (~S3) and extending
to anorectal ring, just proximal to dentate line
Peritoneal covering and Blood supply
- Proximal third: anteriorly and laterally, supplied by superior rectal artery (from IMA) + superior rectal vein to portal system and into liver
- Middle third: anteriorly, and is supplied by middle rectal artery from internal iliac
- Lower rectum is not peritonealized, and is supplied by inferior rectal artery from internal pudendal artery
Middle and inferior rectal tumors spread along middle and inferior rectal veins, into internal iliac lymph nodes, into systemic circulation, and into lung.
Anorectal ring
composed of internal and external sphincters and levator ani muscles
(a) represents internal anal sphincter muscle and is necessary for anal continence,
(b) represents inferior limit for functional sphincter preservation surgery, and
(c) defines lymphatic watershed for rectal cancer spread
Nodal drainage
Superior half of rectum drains along superior rectal artery to pararectal, presacral, sigmoidal, and inferior mesenteric nodes.
Inferior half of rectum drains along middle rectal artery to internal iliac nodes.
Tumors extending to anal canal (below dentate line) may drain to superficial inguinal nodes.
Tumors that invade anteriorly (into pelvic organs) can drain to external iliac nodes.
Most common site of metastasis
Liver
(Liver is the most common site of metastatic disease in both colon and rectal cancers. However, rectal cancer has increased propensity for lung as compared to colon cancer)
Histologies
- Adenocarcinoma 90% (15-20% have colloid- extracellular mucin) (1-2% are signet ring - intracellular mucin with worse prognosis)
- others - small cell, carcinoid, leiomyosarcoma, lymphoma.
Screening (NCCN)
- average-risk patients: colonoscopy at 50 years of age and every 10 years if negative; If polyps identified, repeat colonoscopy every 3 or 5 years depending on risk of polyp. Other options include stool-based testing, CT colonoscopy, or combination of flexible sigmoidoscopy with stool guaiac.
(Stool-based tests include stool guaiac, FIT, or fecal DNA; if positive, proceed to colonoscopy.)
- In high-risk patients, start screening at 40 years of age or 10 years before first diagnosis in affected first-degree relative, then repeat colonoscopy every 5 years.
- If IBD, annual colonoscopy starting 8 to 10 years after symptom onset.
- If FAP, elective colectomy or proctocolectomy after onset of polyposis.
- If HNPCC, colonoscopy every 1 to 2 years starting at 20 to 25 years of age
Surgery
Surgery is mainstay of treatment.
T1 tumors can be initially managed with transanal excision.
All other tumors should undergo transabdominal resection (LAR or APR) with sharp TME with at least 12 lymph nodes resected for staging.
- Local Excision (Transanal Excision or Transanal Endoscopic Microsurgery): Possible for T1 tumors <3 cm in greatest diameter, <30% of rectal circumference, within 8 cm of dentate line or below middle rectal valve, low-grade histology and no LVSI
- LAR: Sphincter-sparing surgery with coloanal anastomosis (or alternatively colonic J-pouch or coloplasty). With modern surgical techniques, distal margin of 2 cm or even less is now adequate and crucial margin is CRM.
- APR: Historically for tumor <5 cm from anal verge where sphincter sparing was not thought possible.
Rectosigmoid is oversewn via abdominal incision and pulled out with anal canal via perineal incision. Requires permanent colostomy. - Total Mesorectal Excision: Standard of care regardless of APR or LAR.
Involves sharp en bloc removal of mesorectum including associated vascular and lymphatic structures, fatty tissue, and mesorectal fascia as “package” through sharp dissection, designed to spare autonomic nerves.
How is locally advanced rectal cancer defined?
● It includes patients with tumors that have grown through the muscularis propria and into the outermost layers of the rectum (T3)
● or through the wall of the rectum, may be attached to other organs or structures (T4),
● and/or are node-positive (N+).
Anatomical extent
Using these anatomical features,
upper rectal cancer includes intraperitoneal tumors,
mid rectal cancers include tumors above the anorectal ring, and
distal (low) tumors have a lower edge of tumor at the level anorectal ring.
T3 Risk stratification
Lower risk T3 (T3a & b): with extramural depth of invasion </= 5 mm- only for upper and mid (local recurrence <5%; 5yr OS - >80%)
Higher risk T3 (c & d) with extramural depth of invasion > 5 mm (local recurrence 20%; 5 yr OS - 40%
- Patients with a low tumor within ie <5 mm of the total mesorectal excision (TME) plane (eg, bordering the intersphincteric
space) or MRF should be considered higher risk.
Whom should TNT be offered for?
- Locally advanced Low rectal cancer ie any T3,4 N+ and/or
- If mid or upper rectal cancers Patients who are at higher risk for local and/or distant metastases,
High risk patients include:
- T4,
- EMVI,
-Tumor deposits identified on MRI
-Threatened MRF, -Threatened intersphincteric plane
For patients with lower risk locally advanced rectal cancer, is CRT or chemotherapy with FOLFOX and selective CRT recommended?
In lower risk locally advanced upper or middle rectal cancer T2N1, T3 N0 to N1 RT can be avoided if they achieve >20% reduction in tumour area after NACT
(PROSPECT phase II/III trial)
