Colorectal cancer Flashcards
What is colorectal cancer?
Malignant adenocarcinoma of the large bowel
Describe the distribution in prevalence between the different types of colorectal cancers
About 66% of new colorectal cancers arise in the colon (43% in the proximal colon and 23% in the distal colon), and 30% occur in the rectum.
Explain the aetiology factors of colorectal cancer
- Environmental and genetic
- There is a sequence of genetic changes that go from normal bowel epithelium to cancer (e.g. APC then COX2 over-expression then K-Ras then p53).
- There is a sequence from epithelial dysplasia to adenoma to carcinoma
- APC gene is a tumour suppressor gene that normally identifies a cell that is accumulating lots of mutations + forces it to undergo apoptosis
- if mutated it can allow for uncontrolled division, leading to polyps
- Polyp makes more mutations more likely, leading to malignant tumours, that will eventually invade tissues
What are the 2 types of polyps?
(can distinguish b/t the 2 by looking at the polyp under a microscope)
1. Adenomatous:
- APC mutation
- cells look normal
2. Serrated:
- Mutations in DNA repair genes
- have SAW-TOOTH appearance
What are the different stages of a colorectal cancer? what category is used for the staging?
- Dukes’ classification for staging (ABCD)- but this is old
OR - Number staging- newer:
stage 0:
- in situ
- not passed mucosa
stage 1:
- beyond mucosa
- no lymph nodes
stage 2:
- entire wall
- may reach nearby organs
- no lymph nodes
stage 3:
- lymph nodes
- no distant organs
stage 4:
- metastatic
- reached distant organs
(if originates in colon, metastasizes to liver, if originates in rectum, travels to the lungs)
What are the risk factors for colorectal cancer?
- Some inherited conditions are associated with high rates of colorectal carcinoma e.g. Familial adenomatous polyposis, Hereditary nonpolyposis/ Lynch syndrome
- elderly & male
- lack of fiber
- Obesity
- Western diet (e.g. red meat, alcohol, low fibre)
- Smoking
- Colorectal polyps, Peutz-Jeghers syndrome
- Previous colorectal cancer
- Family history
- Chronic bowel inflammation e.g. IBD
- Peutz-Jeghers syndrome
Describe the epidemiology of colorectal cancer
- SECOND MOST COMMON cause of cancer death in the West
- 3rd most common cancer and 2nd most common cause of UK cancer deaths
- UK: 20,000 deaths per year
- Average age of diagnosis: 60-65 yrs
What presenting symptoms of colorectal cancer can be picked up on history ?
(Depends on the size and location of the tumour)
1. Left-Sided Colon and Rectum:
- Change in bowel habit
- Rectal bleeding (blood or mucus mixed with the stools)
- Tenesmus (due to a space-occupying tumour in the rectum)
[Tenesmus = sensation of incomplete emptying after defecation]
- Mass PR in 60%
2.Right-Sided Colon:
- Presents later
- Anaemia symptoms (lethargy)
- Weight loss
- Non-specific malaise
- Lower abdominal pain (rare)
IMPORTANT: 20% of tumours will present as an EMERGENCY with pain and distension due to:
Large bowel obstruction
Haemorrhage or peritonitis due to perforation
What signs of colorectal cancer can be found on physical examination?
- Anaemia, especially in R-sided
- Abdominal mass
If metastatic: - Hepatomegaly
- Ascites (shifting dullness)
- Low-lying rectal tumours may be palpable on DRE
What investigations are used to monitor colorectal caner?
- Bloods:
- FBC - anaemia
- LFTs
- Tumour markers (CEA- also used in colorectal cancer to monitor response to chemotherapy- monitors relapse)
- Stools
- Faecal immunochemical test (FIT) every 2 years for men and women age 60-74. If positive patients are referred for colonoscopy. - Imaging:
- Endoscopy
- Sigmoidoscopy (One-off flexible sigmoidoscopy has now been discontinued.)
- Colonoscopy
(This can be used to biopsy the tumour) - Double-Contrast Barium Enema:
- May show ‘apple core’ strictures - Abdominal ultrasound for hepatic metastases
- Contrast CT (less time consuming and more readily available than MRI), imaging is usually conducted after diagnosis, to identify metastasis or other cancers
For staging:
- TNM used
- Patients whose tumours lie below the peritoneal reflection (rectal cancers) should have their mesorectum evaluated with MRI - important in deciding radiotherapy or surgery
- dukes staging (ABCD)- old
What screening tools are used for colorectal cancer?
- FIT test (faecal immunochemical test)
- NHS screening programme for all men and women
- Has replaced FOB (faecal occult blood) test
- EVERY 2 YEARS from 60-74 years
(Flexible sigmoidoscopy screening done in the past- One-off flexible sigmoidoscopy has now been discontinued.)
What is the 2 week-wait criteria for suspected lower GI cancer?
NICE Guidance now recommends faecal immunochemical testing (FIT) to guide referral for suspected colorectal cancer in adults:
- With an abdominal mass
- With a change in bowel habit.
- With iron-deficiency anaemia.
- Aged 40 years and over with unexplained weight loss and abdominal pain.
- Aged under 50 years with rectal bleeding and either of the following unexplained symptoms:
*Abdominal pain.
*Weight loss.
- Aged 50 years and over with any of the following unexplained symptoms:
*Rectal bleeding.
*Abdominal pain.
*Weight loss.
- Aged 60 years and over with anaemia even in the absence of iron deficiency.
If they have a FIT result of at least 10 micrograms, they should be referred for an urgent (within 2 weeks) colonoscopy.
FIT testing should be offered even if they have had a negative result from the screening programme previously.
Adults with a rectal mass should still be considered for a suspected cancer pathway referral (for an appointment within 2 weeks) and do not need a prior FIT test.
How are colorectal cancers treated in a non-emergency setting?
- Surgery: (only curative treatment), depends on circumstances.
- Survival in rectal tumours is improved if total mesorectal excision (removal of surrounding fascia). Isolated hepatic metastases may be successfully resected. - Radiotherapy: May be given in a neoadjuvent setting to downstage rectal tumours prior to resection or as adjuvant therapy to reduce risk of recurrence.
- Chemotherapy: Used as adjuvant therapy in Dukes’ C, or sometimes B:
- 5-Fluorouracil, oxaliplatin and irinotecan are common drugs in first-line chemotherapy protocols; newer agents like cetuximab (monoclonal against EGFR-receptor) and bevacizumab (monoclonal against VEGF) may be considered in metastatic disease or in the context of clinical trials.
What are the different surgeries used to treat colorectal cancers?
- Caecum, ascending colon, proximal transverse colon: Right hemicolectomy.
- Distal transverse colon, descending colon: Left hemicolectomy.
- Sigmoid colon: Sigmoid colectomy.
- High rectum: Anterior resection. >8 cm from the anal canal or involving the proximal 1/3 of the rectum
- Low rectum: Abdo-perineal resection and end colostomy formation. AP resection is the preferred surgical option for tumours <5 cm from the anal verge or involving the distal 2/3 of the rectum
How are colorectal cancers treated in an emergency?
- In an emergency, no primary resection is done for rectal tumours as they have very high rates of anastomotic leaks.
- It needs to be decompressed/defunctioned with a temporary stoma and then the tumour will be staged properly with CT Abdo/Pelvis + MRI Pelvis.
- This will then guide the type of surgery to be done, most likely an APER
- Prior to reversing the ileostomy, to check there are no leaks in the anastomosis, a gastrografin enema is used (preferred over barium as it is less toxic)
- In an emergency situation for a sigmoid tumour (e.g. perforation), perform Hartmann’s procedure (proximal colostomy, resection of tumour and oversew of distal stump).
- In an emergency situation of bowel obsturction= loop colostomy
