Colorectal cancer: Clinical sciences

Colorectal cancer most commonly refers to adenocarcinoma, and it’s usually located in the colon, but it can be found in the rectum as well. The presentation of colorectal cancer is not always clear, so early detection depends on screening. Staging is based on the TNM classification, meaning that tumor size, lymph node invasion, and the presence of metastasis are taken into account when making a treatment plan.

When assessing a patient with signs and symptoms suggestive of colorectal cancer, you should first perform an ABCDE assessment to determine if your patient is stable or unstable. If the patient is unstable, start acute management and stabilize the airway, breathing, and circulation. Next, obtain IV access and initiate IV fluids for resuscitation. Finally, be sure to monitor their vital signs, including pulse oximetry, blood pressure, and heart rate.

Once these important steps are done, you should determine what caused their instability. Tumors located on the descending colon are generally infiltrating masses, meaning they tend to be ring-shaped and involve the whole circumference of the colonic wall. This causes luminal narrowing, referred to as napkin-ring constriction, or apple core lesions because of their appearance on imaging. What's important is that these lesions can lead to an obstruction, which can result in bowel necrosis and perforation.

These patients typically have a history of abdominal pain, nausea, and vomiting; and will also have changes in bowel habits, as well as small caliber or narrow stools described as pencil-thin. On a physical exam, you might find abdominal distention, and signs of peritonitis like rebound pain and guarding. Finally, labs might show leukocytosis. Based on these findings, you should suspect obstruction or perforation caused by the tumor.

Okay, now that we have a diagnosis in mind let’s talk about confirming your suspicion. Your next step is to order an upright abdominal x-ray. You might see large bowel dilatation, which indicates obstruction; and pneumoperitoneum, which means that perforation has occurred. If this is the case, call the surgical team for an emergent laparotomy with resection and send it to pathology, which will provide the final diagnosis.

Okay, before discussing pathology results, let’s go back to H&P to talk about another way colorectal cancer might cause instability. As they grow, some tumors become ulcerated and have fragile blood vessels. If these vessels burst, they may cause acute bleeding. These patients typically present with rectal bleeding and abdominal pain, and may have a history of changes in bowel habits. Additionally, on digital rectal exam, you might see gross blood, and low rectal masses can sometimes be palpated. Finally, labs might show anemia. Based on these findings you should suspect acute GI bleed caused by a colorectal tumor. At this point, you should immediately address the acute bleed and stabilize the patient.

The next logical step is to confirm your diagnosis. To do this, order a colonoscopy with a biopsy. Colonoscopy might reveal overlaying erosion or ulceration, friable mass, synchronous lesions, and active bleeding. If you see these signs, that would mean that the patient has a tumor that caused bleeding. The next step is to get a biopsy to assess the pathology results and determine if the mass is malignant or benign.

Okay, let’s take a look at the pathology results for both patients with perforation, and those with active bleeding. Biopsy showing malignancy leads to a diagnosis of colorectal cancer. However, if there’s no malignancy, consider an alternative diagnosis.

Alright, now that unstable patients are diagnosed, let’s talk about stable patients. The first step here is to obtain a focused history and physical, as well as labs like CBC. Now, patients might present with or without obvious symptoms of colon cancer.

First up, symptomatic patients typically report changes in bowel habits, rectal bleeding, and weight loss. On a physical exam, you might find a palpable abdominal mass, abdominal distention, or tenderness. On a digital rectal exam, you might see gross blood or palpate low rectal masses. Finally, labs might show signs of anemia.

On the other hand, asymptomatic patients might come for several reasons. First, they might have a positive screening fecal occult blood test or fecal immunochemical test. Then, they might come in because of a positive screening colonoscopy. Finally, they might have iron deficiency anemia requiring further workup. In any case, a physical exam is typically unremarkable, while labs might also show signs of anemia.

Here’s a high-yield fact! Some colorectal cancers arise from genetic mutations that can be associated with cancer syndromes. Therefore, be sure to assess for a family history of syndromes like familial adenomatous polyposis, Peutz-Jeghers syndrome, Juvenile polyposis syndrome, Gardner syndrome, Turcot syndrome, and Lynch syndrome.

Okay, with both symptomatic and asymptomatic patients, you should get a colonoscopy with biopsy to find the cause of their symptoms or positive screening tests. Colonoscopy is the most accurate diagnostic test, since it allows to localize and biopsy lesions throughout the large bowel, detect synchronous neoplasms, and remove polyps. If a full colonoscopy can’t be performed because of obstruction, they may need surgical intervention to resect the obstructing mass, and the surgeon can do a colonoscopy in the operating room if needed.

Logically, if there are no masses or signs of colorectal cancer on colonoscopy, or if biopsy results are negative, consider an alternative diagnosis. Now, the vast majority of colorectal cancers are endoluminal masses that arise from the mucosa and protrude into the lumen. They may be exophytic or polypoid in nature, and may be friable, necrotic, or ulcerated with associated bleeding. Additionally, the biopsy is positive for malignancy.

Once the diagnosis of colon cancer is made, you can move on to TNM staging with a CT of the chest, abdomen, and pelvis. Cancer staging is based on the TNM system, which stands for Tumor size and extent, spread to Lymph Nodes, and Metastasis or spread to distant parts of the body. The treatment depends on the TNM stage. In general, early-stage cancers can be resected with surgery, while advanced-stage cancers may require different combinations of chemotherapy, radiation, and surgery when possible. Next to TNM staging, you should obtain carcinoembryonic antigen, or CEA, to get a baseline, which will help you follow if the treatment is working or not down the line, as well as if there’s a recurrence.