Colorectal/anal cancer Flashcards
Epidemiology of colorectal cancer
2nd most common cancer diagnoses
2nd leading cause of death of cancer in men
3rd leading cause of death of cancer in women
incidence higher in men than women - incidence rates are declining due to screening
Etiology of colorectal cancer
Diet low in fibre or calcium high in fat or phosphate
- a diet high in processed meats and red meats has been associated with a high risk
Obesity
Smoking
Excessive alcohol drinking
Family history
- having a first degree relative with colorectal cancer
Inflammatory bowel disease
- Crohn’s disease: 2% developed cancer in 10 years
- ulcerative colitis: 20% in 10 years
Adenomatous polyps
Hereditary cancer syndromes:
- familial adenomatous polyposis
- hereditary nonpolyposis colorectal syndrome or Lynch syndrome
Eight regions of the colon
- cecum
- ascending colon - immobile, retroperitoneal
- descending colon - immobile, retroperitoneal
- splenic flexure - immobile, retroperitoneal
- hepatic flexure -immobile, retroperitoneal
- transverse colon
- sigmoid
- rectum - continuous with the sigmoid and begins at the level of the third sacral vertebrae
Four main layers of the large bowel
Mucosa
Submucosa
Muscularis propria
Serosa
These layers are used in the staging system to define the involvement through the bowel wall.
Mucosa
The innermost layer forms the lumen of the bowel wall.
Consists of two supporting layers:
- lamina propria
- muscularis mucosa
Submucosa
Second most inner layer. Is rich with blood vessels and lymphatics.
Muscularis propria
Contains two muscle layers, one circular and one longitudinal which are responsible for peristalsis. Beneath the muscularis layer is a layer of fat termed the subserosal layer.
Serosa
The outermost layer. Not all segments of the colon have a serosa layer. This layer is provided by the visceral peritoneum.
Ascending colon lymphatic drainage
Follows the superior mesenteric vessels.
- ileocolic
- right colic nodes
- pericolic
- middle colic
Hepatic (right colic) flexure lymph drainage
- pericolic nodes
- middle colic nodes
- right colic nodes
- ileocolic nodes
Cecum lymphatic drainage
- pericolic
- anterior cecal
- posterior cecal
- ileocolic
- right colic
Transverse colon lymphatic drainage
- pericolic nodes
- middle colic nodes
Splenic (left colic) flexure lymph node drainage
- pericolic
- middle colic
- left colic
- inferior mesenteric nodes
Descending colon
- pericolic nodes
- left colic nodes
- inferior mesenteric nodes
- sigmoid nodes
Sigmoid colon lymph drainage
- pericolic
- perirectal
- sigmoid mesenteric
- inferior mesenteric
- superior rectal
Rectum lymph drainage
Upper 1/3 –> superior rectal nodes –> sigmoid mesenteric nodes –> inferior mesenteric nodes
Middle and lower 1/3 –> middle and infererior rectal nodes –> internal iliac nodes
Other nodes: obturator, lateral sacral, presacal, sacral promontory nodes.
Clinical presentation of colorectal cancer
Abdominal pain
Change in bowel habits
- pencil-thin stool, constipation or diarrhea may indicate obstructive tumour
- more common with left-sided colon cancer
GI bleeding
- more common with right-sided colon cancer
Isolated anemia
Weightloss
Colorectal cancer screening
A person of average risk beginning at 50 should undergo a fecal immunochemical test, flexible sigmoidoscopy, double-contrast barium enema, or CT every 5 years. A colonoscopy should follow up any positive results.
A person with genetic factors should undergo colonoscopies before the age of 50
Colonoscopy
Should be done every 10 years. Examines the entire colon and can visualize polyps and allow them to be removed for examination.
High sensitivity for detecting mucosal regions.
A newer technique called 3D-colonoscopy uses a CT scanner and 3D software which examine the inside of the colon without the lengthy scope. Has the same radiation exposure as a barium enema.
Flexible sigmoidoscopy
Evaluation of splenic flexure only.
Up to 66% of tumours can be missed due to incomplete bowel evaluation.
Capsule endoscopy
Ingested capsule provides a photographic evaluation of colon and rectum
Double-contrast barium enema
Useful in patients with incomplete colonoscopy
Requires additional procedure for the intervention of biopsy.
Detects only 20% of polyps found on colonoscopy
Proctosigmoidscopy
Is performed after detection with colonoscopy can provide a more accurate depiction of the size and location of the lesion.
Pathology of colorectal carcinoma
Adenocarcinoma accounts for 90-95% of all cancer.
Other histologic types include:
- mucinous adenocarcinoma
- signet-ring cell carcinoma
- squamous cell carcinoma
Tis colorectal cancer
Intraepithelial or invasion of lamina propria
T1 colorectal cancer
Tumour invades submucosa
T2 colorectal cancer
Tumour invades muscular propria
T3 colorectal cancer
Tumour invades through muscularis propria into the peri-colorectal tissues
T4 colorectal cancer
T4a: penetrates to the surface of the visceral peritoneum
T4b: tumour directly invades or is adherent to other organs or structures.
N1 colorectal cancer
Metastasis to 1 to 3 regional lymph nodes
N1a: metastasis to 1 regional lymph nodes
N1b: metastasis to 2 or 3 regional lymph nodes
N1c: Tumour deposits into the subserosa, mesentery or nonperitonealized pericolic or perirectal tissues without regional node metastasis
N2 colorectal cancer
Metastasis into 4 or more regional lymph nodes
N2a: metastasis in 4 or 6 regional nodes
N2b: metastasis in 7 or more regional nodes
M1 colorectal cancer
M1a: metastasis confined to one organ or site
M1b: metastasis in more than one organ or the site or in the peritoneum
Routes of spread for colorectal cancer
Local spread: penetration of bowel wall and invasion of adjacent organs
Perineural invasion: local spread may be as far as 10cm from the primary tumour
Lymphatics
Liver and lungs are most common sites of hematogenous metastasis
Surgery of colorectal cancer
Surgery is considered the treatment of choice. The tumour and adequate margin and lymphatics are removed.
The two most common rectal surgeries are:
- lower anterior resection
- abdominoperineal resection
Low anterior resection (LAR)
Removal of tumour plus margins as well as regional lymphatics. The bowel is anastomosed therefore a colostomy is not necessary. Used to treat colon cancer and some rectal cancers.
Abdominoperineal resection (APR)
Used for patients with rectal cancers in the lower distal third of the rectum.
An anterior incision is made into the abdominal wall to make a colostomy.
Then a perineal incision is made to resect to rectum, anus and drainage lymphatics with the entire enbloc removed through the incision.
Finally, the reperitonilization is done for patients who have post-operative radiotherapy to pull the small bowel more superior and reduce toxicity after RT.
Radiation therapy for colorectal cancer
Most commonly used adjuvant treatment for colorectal cancer. Can be done before or after surgery or in conjunction with chemotherapy.
Post-operative RT colorectal cancer
Concurrent chemotherapy is advocated based on the high local failure rate of surgery alone with patients who have nodal involvement or tumour extension beyond the rectal wall.
Post-op RT with chemotherapy has been shown to improve local control and survival rates in patients with rectal cancer.
The advantage to post-op RT is the oncologist has the pathological information of the tumour and the extent of spread as well as nodal information.
Pre-operative RT for colorectal cancer
Common for patients who have large rectal cancers that have invaded through the muscle layer (T3) or have enlarged lymph nodes (N1 or N2).
The goal of this is sphincter preservation. This is done to shrink the tumour and then a LAR can be done instead of APR, therefore reducing the need for colostomy.
A disadvantage is there is no pathology information on the tumour before beginning RT.
Common TDF’s colorectal cancers
Dose to large volume: primary + LN’s is 4500cGy
Dose to primary tumour bed: 5000 to 5500cGy in 6 to 6.5 weeks.
Doses of over 5000cGy are not achievable unless the small bowel is out of the treatment field.
Treatment volume colorectal cancer
Sup: L5-S1 (with more advanced disease may go up to L4)
Inf: includes the entire obturator foramina. (or 3-5cm below gross tumour before resection)
Lateral: 2cm lateral to the pelvic brim
Ant: behind the pubic symphysis
Post: 2cm behind sacrum to include pre-sacral LN’s
Prognostic factors of colorectal cancer
Patients who had pre-op RT do better
Lymphatics and venous invasion are adverse factors
Patients with tumours around the peritoneal reflections either rectosigmoid or rectum have a worse 5-year survival
5-year survival:
symptomatic patients: 49%
Asymptomatic patients: 71%
Epidemiology of anal cancer
More common in women than men.
General age distribution in 30-90 years with a median age of 60.
Men younger than 45 have seen a rise in rates of anal cancer most likely contributed to anal sex and HPV.
Etiology of anal cancer
Genital warts
Genital infections
HPV
Anal intercourse in men or women before the age of 30
Smoking has also seen to increase the chance of anal cancer
Anatomy of anal canal
3-4cm long extends from the anal verge to the anorectal ring at the junction of the anus and the rectum.
Lymphatics of the anal canal
Initially to the perirectal and anorectal lymph nodes.
If the tumour extends above the dentate lime the lymph nodes at risk are:
- internal iliac nodes
- lateral sacral nodes
If the tumour extends below the dentate lime the lymph nodes at risk are:
- inguinal nodes
Dentate line
Divides the upper 2/3 of the anal canal from the lower 1/3 of the anal canal
Clinical presentation of anal cancer
The most common presenting symptom is rectal bleeding (bright red).
Other symptoms may include pain, bowel changes and the sensation of a mass.
Detection and diagnoses of anal cancer
Digital anorectal exam and palpation of inguinal nodes
Anoscopy or proctoscopic examination and biopsy should also be obtained.
Pathology of anal cancer
Squamous cell carcinoma is the most common histology of anal cancer.
Basaloid (cloacogenic) cancers are the next most frequent pathology occurs around the dentate line where the epithelium changes.
Adenocarcinoma may be diagnosed in the anal glands.
T1 stage anal cancer
Tumour 2cm or less in greatest dimension
T2 stage anal cancer
Tumour more then 2cm but less then 5 in greatest dimension
T3 stage anal cancer
Tumour greater then 5cm in greatest dimension
T4 stage anal cancer
Tumour of any size invades adjacent organs (vagina, urethra, bladder).
N1 stage lymph nodes
Metastasis in perirectal lymph nodes
N2 stage anal cancer
Metastasis in unilateral internal iliac or inguinal lymph nodes
N3 stage anal cancer
Metastasis in perirectal and inguinal nodes or bilateral internal iliac or inguinal nodes
Routes of spread for anal cancer
Most frequently via direct extension into adjacent soft tissues.
Lymphatic spread occurs relatively early to pelvic nodes but more commonly to inguinal nodes.
Hematogenous spread to liver and lung is less common
Chemotherapy associated with anal cancer
5-FU and mitomycin C is the most common treatment along with radiation
Cisplatin is also used with 5-FU and typically has less side effects.
A most common treatment for anal cancer
Chemoradiation is the preferred treatment this has been shown to provide good local control and colostomy-free survival.
Radiation alone is an option for those who can not handle chemoradiation.
Most common surgical procedure for anal cancer
Abdominoperineal resection with a wide perineal dissection is the most common. Although no longer the initial treatment of anal cancer. Done if local recurrence after chemoradiation.
Field borders anal cancer
Sup: L5-S1
Inf: 3cm below the anal marker
Lat: 1.5-2cm from the pelvic brim
TDF for anal cancer
RT alone: 6000 to 6500cGy to pelvis with a field reduction and 4500cGy primary tumour to reduce small bowel toxicity.
Combined modality: 4500cGy with a smaller field boost of 1440cGy to 2440cGy to primary tumour
Most common side effects of RT for anal cancer
Perineal skin reaction, nausea, vomiting and diarrhea are most reported.
