Theodore S. Hong
EPIDEMIOLOGY
In 2013 there were approximately 143,000 Americans diagnosed with colon and rectal cancer. Approximately 2/3 will involve the colon and 1/3 the rectum. Epidemiological factors and pathogenesis are similar for rectal cancer as for colon cancer.
ANATOMY
The rectum is generally divided into three portions: lower rectum, mid-rectum, and upper rectum. The distances from the anal verge are approximations and may vary with flexible endoscopic techniques.
• Lower rectum: 4–8 cm from anal verge
• Mid-rectum: 8–12 cm from anal verge
• Upper-rectum: 12–16 cm from anal verge
• Anal canal: 4 cm in length
IMPORTANT LANDMARKS
Dentate Line
The dentate line is the transition point between the squamous mucosa of the anus/perineum and the columnar mucosa of the rectum. Below the dentate line, the lymph drainage flows through the inguinal nodes and has implications for treatment.
Rectum/Sigmoid Boundary
In contrast to the sigmoid colon, peritoneum does not cover the circumference of the rectum. Rectal cancer has higher rates of local failure following surgery than colon cancer and requires aggressive local treatment.
Generally, rectal tumors should be no less than 6–7 cm from anal verge if a sphincter sparing operation is to be attempted in order to preserve muscle function while obtaining adequate margins.
DIAGNOSIS AND STAGING
DIAGNOSIS
Presenting Symptoms
The majority of patients diagnosed with rectal cancer present with symptoms, although many are nonspecific and this may lead to a delay in diagnosis. Common symptoms include bleeding (gross or occult), constitutional symptoms, abdominal pain, changes in stool caliber, and changes in bowel habits.
WORKUP
When cancer is in the differential diagnosis, the workup entails history and physical including digital rectal examination (DRE), complete blood count, liver and renal function tests, carcinoembryonic antigen (CEA), and endoscopy.
DRE DRE should be used to assess the location of the tumor in relation to the anal verge, the dentate line, and the anal sphincter. If possible, the tumor should be assessed with respect to anal sphincter involvement, circumferential extent, and possible fixation to normal structures. Baseline sphincter tone should be assessed.
Rigid proctosigmoidoscopy This is used both to assess the location of the tumor (especially when nonpalpable), and to take biopsies for tissue diagnosis.
STAGING
Staging system
Rectal cancer is staged using clinicopathological parameters and classified using the AJCC TNM system (see Table 47-1). Preoperative staging is used for prognostic purposes and to estimate the risk of recurrence after surgery to guide adjuvant therapy.
T and N Stage
Endorectal ultrasound and MRI are commonly used to assess the extent of the primary tumor. Nodal status can be determined using MRI, CT, and EUS, but may be difficult to assess radiographically.
Endorectal Ultrasound (Eus)
EUS is able to distinguish the five layers of the rectal wall with good spatial resolution. The accuracy for T stage ranges from 67% to 97% with a propensity to overstage tumors as indicated by a reported specificity of 24% for peri-rectal penetration. EUS is operator dependent and associated with a fast learning curve (1, 2).
Magnetic Resonance Imaging (Figure 48-1)
FIGURE 48-1 (Clockwise from lower left) sagittal, axial, and coronal T2 weighted MRI of the pelvis showing a rectal tumor invading through the muscularis propria (MP) making this a T3 lesion.
When MRI is used for primary determination of T stage, a surface phased array coil is employed enabling differentiation of rectal wall layers. Accuracy is operator dependant with interrater accuracies in one study of 67% and 83%. MRI can also be used for preoperative assessment of the likely circumferential margin (CFM) following surgery. The accuracy of N stage evaluation is similar to that of CT in that both are based on size criteria (3).
Assessment of Metastatic Disease
Computed tomography (CT) CT is used primarily for preoperative assessment of metastatic disease in the lungs, liver, or abdomen. It is less useful for the assessment of T stage with accuracy rates of only 33%–77% resulting from the inability to distinguish layers of rectal wall. The sensitivity for detection of nodal disease ranges from 45% to 73% (1).
Residual or Recurrent Disease
Positron emission tomography may be used for the assessment of residual or recurrent disease and may be helpful in areas of scarring or radiation changes (1).
TREATMENT
A general treatment algorithm is included in Figure 48-2.
FIGURE 48-2 Treatment algorithm. The type of surgery (LAR, APR) depends on the location of the tumor and the ability to spare the anal sphincter while maintaining adequate surgical margins. Chemoradiation consists of 5FU given concurrently with radiation to a pelvic field.
SURGICAL MANAGEMENT
Local Excision
A number of criteria must be met in order to proceed with local excision. These include T1 without evidence of nodal disease, tumor within 4–6 cm of the anal verge, and involvement of less than 40% of circumference of bowel wall. Histopathological limitations include well to moderately differentiated histology and no evidence of lymphovascular invasion. Local excision techniques must be full-thickness excisions. These include transanal excision, posterior proctoctomy, and transsphincteric excision. The role of local excision for T2 tumors is highly controversial.
ABDOMINAL PERINEAL RESECTION (APR)
An APR is a nonsphincter sparing operation requiring both an abdominal and perineal incision and a permanent colostomy. It is the standard procedure for tumor removal when the lower extent of the tumor does not allow for sphincter preservation with adequate tumor margins (traditional margin is 5 cm, although 2-cm margins have been used). The entire rectum along with the sphincter apparatus is removed through the perineum.
LOW ANTERIOR RESECTION (LAR)
LAR involves the mobilization of the entire rectum and complete resection of the involved segment of the rectum encompassing the tumor with a margin. The remaining ends are reanastomosed, so that no permanent colostomy is required.
Total Mesorectal Excision (Tme)
Prior to TME, traditional surgical techniques invaded tissue planes during blunt dissection. The CFM status following surgery correlates with the risk of local recurrence. TME requires sharp dissection under direct visualization to remove the entire rectal mesentery along with the peri-rectal fat as one discrete unit. This procedure has improved outcomes (4).
Combined Modality Therapy
Combined modality therapy is considered either when the risk of local recurrence is significant (stage II–III disease) or in an attempt to covert an APR to a sphincter sparing operation. When chemotherapy and radiation are used in addition to surgery for local disease control, fluoropyrimidine-based chemotherapy must be used for systemic therapy following surgery. Major adjuvant and neoadjuvant trials are listed in Table 48-1.
TABLE 48-1 MAJOR ADJUVANT AND NEOADJUVANT TRIALS
Neoadjuvant Therapy
Although survival was identical between the two arms, the Dutch Colorectal Cancer Group trial showed that in patients undergoing surgery with TME, preoperative radiation was associated with decreased rates of local recurrence (5). Trials with preoperative chemoradiation improved on the results of preoperative radiation. Chemoradiation has also been used preoperatively to convert tumors requiring APR into sphincter sparing procedures.
Adjuvant Therapy
In the mid-1980s, the Gastrointestinal Tumor Study Group (GITSG) showed that adjuvant chemoradiation was associated with a survival benefit when compared with no further treatment following surgery (6). This and other trials led the NIH to recommend adjuvant chemoradiotherapy for patients with stage II or III disease in 1990.
Neoadjuvant versus Adjuvant Therapy
The question of whether pre- or postoperative chemoradiation provided the most benefit was asked by the German Rectal Cancer Study Group. At 5 years of follow-up, preoperative chemoradiation was associated with a lower rate of local recurrence (6% vs. 13%), a lower rate of grade 3 or 4 acute toxic effects (27% vs. 40%), and lower rate of long-term toxic effects (14% vs. 24%). There was no difference in overall survival. Preoperative chemoradiation also allowed for greater sphincter sparing (7). Long-term follow-up of this study confirms the local recurrence benefit with preoperative therapy at 10 years (7.1% vs. 10.1%) (8). The National Surgical Adjuvant Breast and Bowel Project (NSABP) R-03 also demonstrated a 5-year disease-free survival benefit with preoperative chemoradiation versus postoperative chemoradiation (64.7% vs. 53.4%) (9). Standard preoperative chemoradiation includes 50.4 Gy in 1.8 Gy fractions given with continuous infusion 5FU (225 mg/m2).
Preoperative Short Course Radiation Alone versus Standard Chemoradiation
Preoperative short course radiation therapy, as given in the Dutch Colorectal Cancer Group trial, has been compared to preoperative chemoradiation, as given in the German Rectal Study and NSABP R-03. Short course radiation uses five fractions of radiation alone (5 Gy × 5), with surgery the following week. Two randomized trials show no difference in survival, local control, or late toxicity (10, 11).
Unresectable Disease
Neoadjuvant chemoradiation can be used to convert unresectable disease into resectable disease. If there is residual disease or if there is a strong possibility of positive margins, intraoperative radiation therapy (IORT) may be considered.
Recurrent Disease
There are no clear data on the management of recurrent disease. If surgical resection is possible with negative margins, long-term survival is possible. Reirradiation can be associated with high rates of complications as a function of the radiation dose and time interval from prior treatment.
Metastatic Disease
The foundation of the treatment of metastatic disease is fluoropyrimidine-based chemotherapy and is similar to the treatment of metastatic colon cancer (see chapter on colon cancer for details).
SURVEILLANCE AND FOLLOW-UP
• History and physical. Every 3–6 months for the first 3 years, every 6 months for years 4 and 5, and at the discretion of the physician thereafter.
• Proctosigmoidoscopy. Every 6 months for 5 years in patients not treated with radiation.
• CEA. Every 3 months for 3 years; fluorouracil-based chemotherapy may cause false elevation.
• Chest/Abdomen/Pelvic CT should be considered once a year for 3 years.
REFERENCES
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