Colorectal Cancer Flashcards
How common is colorectal cancer?
Colorectal cancer is the fourth most common cancer in the UK, with around 40,000 new cases each year, and the second highest mortality of any cancer. It accounts for approximately 10% of all diagnosed cancers and cancer-related deaths worldwide, with the highest rates seen in the more developed countries.
Briefly describe the pathophysiology of colorectal cancer
Colorectal cancers originate from the epithelial cells lining the colon or rectum, most commonly an adenocarcinoma. Rarer types include lymphoma (~1%), carcinoid (<1%) and sarcoma (<1%).
Most colorectal cancers develop via a progression of normal mucosa to colonic adenoma (colorectal ‘polyps’) to invasive adenocarcinoma (termed the “adenoma-carcinoma sequence”). Adenomas may be present for 10 years or more before becoming malignant; progression to adenocarcinoma occurs in approximately 10% of adenomas.
Certain genetic mutations have been implicated in predisposing individuals to colorectal cancer.
Give examples of genetic mutations linked to colorectal cancer
Adenomatous polyposis coli (APC)
- A tumour suppressor gene, mutation of the APC gene results in growth of adenomatous tissue, such as Familial Adenomatous Polyposis (FAP)
Hereditary nonpolyposis colorectal cancer (HNPCC)
- A DNA mismatch repair gene, mutation to HNPCC leads to defects in DNA repair, such as Lynch syndrome
Briefly describe the adeno-carcinoma sequence
What are the risk factors for colorectal carcinoma?
Approximately 75% of colorectal cancers are sporadic, developing in people with no specific risk factors.
However, potential risk factors include increasing age, male gender, family history (positive family history is present in 10–20% of all patients with colorectal cancer), inflammatory bowel disease, low fibre diet, high processed meat intake, smoking, and excess alcohol intake.
What are the clinical features of colorectal cancer?
The common clinical features of bowel cancer include change in bowel habit, rectal bleeding, weight loss, abdominal pain and symptoms of (iron-deficiency) anaemia.
Briefly differentiate the clinical presentation of left and right sided colon cancers
Right-sided colon cancers: abdominal pain, iron-deficiency anaemia, palpable mass in right iliac fossa, often present late.
Left-sided colon cancers: rectal bleeding, change in bowel habit, tenesmus, palpable mass in left iliac fossa or on PR exam.
Briefly describe the NICE guidelines regarding when patients need referrel for urgent investigations in suspected bowel cancer
In the UK, NICE guidance recommends that patients should be referred for urgent investigation of suspected bowel cancer if:
- 40yrs with unexplained weight loss and abdominal pain
- ≥50yrs with unexplained rectal bleeding
- ≥60yrs with iron‑deficiency anaemia or change in bowel habit
- Positive occult blood screening test
What investigations should be ordered for colorectal cancer?
Note: laboratory investigations
Routine bloods should be performed for all suspected cases. A full blood count (FBC) may show a microcytic anaemia (an iron-deficiency anaemia), as well as LFTs and clotting.
The tumour marker Carcinoembryonic Antigen (CEA) should not be used as a diagnostic test, due to poor sensitivity and specificity, however it is used to monitor disease progression and should be conducted both pre- and post-treatment, screening for recurrence.
What investigations should be ordered for colorectal cancer?
- Note: imaging
The gold standard for diagnosis of colorectal cancer is via colonoscopy with biopsy. If a colonoscopy is not suitable for the patient, such as from frailty, co-morbidities or intolerance, CT colonography can be performed for initial diagnosis.
Once the diagnosis is made, several other investigations are required (primarily for staging):
- CT scan (Chest/Abdomen/Pelvis) to look for distant metastases and local invasion
- MRI rectum (for rectal cancers only) to assess the depth of invasion and potential need for pre-operative chemotherapy
- Endo-anal ultrasound (for early rectal cancers, T1 or T2 only) to assess suitability for trans-anal resection
What is the role of biopsies in colorectal cancer?
Biopsy samples being sent for histology will be assessed using TNM staging, histological subtyping, grading, and assessment of lymphatic, perineural, and venous invasion. Increasingly, samples are also routinely being assessed for varying tumour-based markers (including mismatch-repair testing), to aid in the identification of Lynch syndrome and to optimise potential chemotherapy regimes.
What is shown in the image?
Endoscopic image of colorectal adenocarcinoma.
Briefly describe the staging of colorectal cancer
Colorectal cancer is staged according to the TNM system. This stages the cancer according to the depth the tumour invades the bowel wall (T stage), the extent of spread to local lymph nodes (N stage), and whether or not there are distant metastasis (M stage).
Whilst the Duke’s staging system has now been largely superseded, it is still used at some centres for additional staging detail.
Briefly describe Duke’s Staging
A: confined beneath the muscularis propria
B: extension through the muscularis propria
C: involvement of regional lymph nodes
D: distant metastasis
Briefly describe the general management of colorectal cancer
All patients should be discussed with the multidisciplinary team (MDT).
The only definitive curative option is surgery, although chemotherapy and radiotherapy have an important role as neoadjuvant and adjuvant treatments, alongside their role in palliation.
What procedure is used in emergency bowel surgery (such as bowel obstruction or perforation)?
Hartmann’s Procedure.
This procedure is used in emergency bowel surgery, such as bowel obstruction or perforation. This involves a complete resection of the recto-sigmoid colon with the formation of an end colostomy and the closure of the rectal stump.
