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Workup and Evaluation of Patients with Rectal Cancer

April 10, 2023 - read ≈ 10 min



Brian C. Brajcich, MD MS

Department of Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL, USA


Vitaliy Y. Poylin, MD

Department of Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL, USA



Rectal cancer is among the most common malignancies, making up 9.4% of all new cancer diagnoses with an estimated worldwide incidence of over 700,000 cases in 2020.[1, 2] Rectal cancer is also one of the deadliest cancers, ranking 10th in mortality among cancer sites and resulting in nearly 340,000 deaths in 2020.[1, 2]

Aside from death, rectal cancer also results in substantial morbidity related to bleeding, obstruction, perforation, and metastatic spread. The incidence of rectal cancer varies little across globe, although some evidence suggests that its incidence is higher in developed countries, possibly associated with physical inactivity, western dietary patterns, and obesity.[3]

The incidence of rectal cancer has been increasing for unknown reasons over the past 30 to 40 years in many regions, particularly among younger individuals.[4-6] Because of these factors, rectal cancer is an important health condition and warrants adequate resources for treatment.

The treatment of rectal cancer has historically been defined by surgical resection of the tumor, although this has had mixed success due to high rates of surgical complications and recurrence. In recent decades, however, numerous trials have demonstrated the utility of a multidisciplinary treatment approach consisting of surgical resection, systemic therapy, and external beam radiation.[7]

With these advances in treatment and improved rates of screening colonoscopy, the treatability of colorectal cancer has improved dramatically, with the 5-year survival rate increasing from 50% in the 1970s to 64% from 2009 through 2015.[5] However, significant gaps in the diagnosis and treatment of rectal cancer persist globally.[8]

Modern multimodal treatment regimens are dependent on comprehensive preoperative diagnostic and staging evaluations, which may be difficult to complete in resource-limited settings. This chapter aims to summarize the diagnosis and initial work-up of patients with rectal cancer, and to review optimal and acceptable diagnostic approaches for these complex patients in settings with varying amounts of medical resources.


When screening tests such as colonoscopy are available, rectal cancer is often able to be identified prior to the development of symptoms, and in many cases, premalignant polyps may be able to be removed before they progress into cancer.(9) However, many patients are diagnosed with rectal cancer after developing symptoms related to their tumor, and it is therefore important for the clinician to be familiar with the common presenting features of rectal cancer.

The signs and symptoms of rectal cancer can be categorized into several discrete groups. Many patients experience symptoms related to the local mass effect of the tumor. This may include feelings of tenesmus or a palpable or prolapsing mass (particularly for very low rectal cancers).

Over time, increased stool frequency, the sensation of incomplete evacuation, and mucus discharge can develop. Additionally, patients with advanced lesions can experience symptoms of partial or complete obstruction. These symptoms include narrow caliber stools, constipation and bloating, and eventually obstipation.

With a complete large bowel obstruction, patients are at risk for colonic perforation if a competent ileocecal valve is present. Patients with mucosal-based tumors such as rectal cancer can also present with bleeding, either acutely (in the form of hematochezia) or in a subclinical fashion such as iron deficiency anemia. It is for this reason that iron deficiency anemia in an older individual (especially in a post-menopausal female) warrants diagnostic evaluation for an occult colorectal malignancy as the etiology.

Finally, patients can present with systemic signs and symptoms, such as fatigue or unexpected weight loss. These symptoms are more common with advanced disease and may also be accompanied by sequelae specific to disseminated disease, such as ascites, liver failure or pulmonary symptoms.

Diagnostic workup

Initial diagnosis

The diagnostic workup for rectal cancer is divided into two phases. First, the diagnosis of rectal cancer must be made and confirmed histologically, and second, the patient must be clinically staged to guide treatment. Generally, the diagnosis of rectal cancer is made following an endoluminal examination of the rectum by flexible or rigid endoscopy. This may occur during a screening procedure or may happen as part of testing to identify the cause of one or more of the aforementioned signs or symptoms.

The location of the tumor in relation to the anal sphincter complex is an important factor in their management. Digital exam should be performed in all cases of rectal cancer and the distal extent of the mass on exam should be documented. Any polyps or suspicious masses noted on evaluation should be resected in their entirety if possible, and if not, should be biopsied and undergo routine histopathologic testing. If possible, the entirety of the colon should be examined to assess for synchronous lesions.

Histologic and molecular testing

Important aspects of pathologic analysis include whether the margins of the specimen are free of malignancy if the lesion was resected in its entirety, the presence or absence of lymphovascular invasion, and the histologic type and grade of the tumor. Recent guidelines recommend routine molecular testing of all new colorectal cancers for microsatellite instability using polymerase chain reaction or next generation sequencing, or testing for the absence of mismatch repair proteins using immunohistochemistry.[10]

If routine testing is not available, selective testing genetic testing should be attempted in patients with a suspicious family history of malignancy.

Clinical staging

Once the diagnosis of rectal cancer is established, the patient should be appropriately staged as the tumor stage plays vital role in the diagnostic process and determines potential treatment options. Rectal cancer staging is based on the TNM staging system.[11]

T-stage is determined by the depth of tumor invasion into the rectal wall and perirectal tissues while N-stage is determined by the presence of metastasis to locoregional lymph nodes.

M-stage is determined by spread to distant organs, most commonly the liver, lungs, or peritoneal cavity. M-staging is best assessed by computed tomography (CT) imaging of chest, and of the abdomen and pelvis with intravenous contrast. If CT is not available, chest radiograph and liver ultrasound are alternative options for staging but have significantly lower sensitivity and specificity.

CT is not a reliable modality to determine T– and N-stage.[12] Dedicated pelvic magnetic resonance imaging (MRI) is the preferred modality with superior evaluation of the mesorectal fascia and therefore an increased ability to predict whether the circumference resection margin (CRM) will be involved by tumor (sensitivity of 60-88% and specificity of 73-100% for histologically positive CRM).[13]

Endoscopic ultrasound (EUS) is an alternate modality for T– and N-staging, with improved accuracy for accurate T-staging of early stage (T1 and T2 cancers). [12] However, EUS is operator dependent and is unable to reliably assess mesorectal fascia involvement.

MRI and EUS are comparable in their ability to detect mesorectal lymph node metastasis, with 66% sensitivity and 76% specificity for MRI compared with 67% sensitivity and 78% specificity for EUS.[12]

Additional information provided by staging imaging includes whether the tumor invades adjacent pelvic structures and the relationship of the tumor with the anal sphincters, both of which determine the resectability of the tumor and the appropriate surgical approach. Positron emission tomography (PET) scans are generally not indicated during rectal cancer staging. Repeat imaging after neoadjuvant treatment but before surgery remains controversial and should be approached individually based on specific areas of concern on the initial imaging.

Controversies and limitations

It is important to appreciate that, although staging imaging can provide valuable information about local, regional, and distant progression of disease, it is not a substitute for pathologic analysis. This is particularly true regarding spread to regional lymph nodes, as even the best imaging modalities are limited in their sensitivity to detect lymph node metastasis.

For that reason, surgical resection is typically indicated for staging purposes as well as for treatment of the primary tumor. Recent evidence has suggested that pathologic staging, as well as resection, may be foregone in select cases of rectal cancer with complete radiographic response of the tumor to neoadjuvant therapy.[14]

However, such an approach is dependent on access to optimal initial staging and surveillance modalities, and therefore cannot be recommended in regions where these resources are not readily available. In these cases, pathologic staging of the primary tumor and regional lymph nodes is an essential component of the staging workup along with radiologic evaluation.


Rectal cancer has a high worldwide incidence and is responsible for significant rates of mortality and morbidity. Suspicion for rectal cancer must be high among patients with hematochezia, tenesmus, iron deficiency anemia, or unexplained changes in bowel habits.

Treatment of rectal cancer depends on adequate histologic evaluation and radiologic staging, ideally with cross-sectional imaging. Optimal pre-operative evaluation of rectal cancer includes endoscopic evaluation of the entire colon with histologic diagnosis of the lesion and testing for microsatellite instability or mismatch repair enzyme deficiency.

Ideal staging additionally entails CT imaging of the chest, abdomen, and pelvis and dedicated pelvic MRI. Accurate staging is essential, as it determines the surgical approach and guides multimodality treatment.


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