Local Treatment of Rectal Cancer

Introduction

The treatment of early rectal cancer has been a controversial subject for several decades. Radical proctectomy with total mesorectal excision (TME) is the gold standard for patients with tumors localized to the bowel wall. The average local recurrence (LR) rate for stage I rectal cancer after TME approximates 2%, and 5-year survival is as high as 95%. However, the morbidity associated with radical proctectomy is considerable, with postoperative complication rates approaching 35%, and the mortality rate after abdominal perineal resection (APR) has been reported to be up to 5%. Both low anterior resection (LAR) and APR are associated with significant rates of long-term sexual and urinary dysfunction. Bowel function after restorative resection is compromised in at least one third of all patients, and after APR, creation of a permanent stoma is associated with an 80% risk of long-term complications.

Local excision (LE) of rectal cancer was first introduced by Kraske in the 1880s. It did not become popular until the 1960s, when Mason introduced the transsphincteric approach. The posterior transsphincteric approach is well suited to distal tumors located in the anterior wall of the rectum. In many centers, Mason’s procedure is the preferred approach for the repair of recto-ureteral fistulae because of the access it provides. Fecal incontinence is the main complication, although rates of less than 1% have been reported in some series.

Parks was the first to describe transanal excision (TAE) without division of the anal sphincter for rectal cancer, using a specially designed set of speculums to gain access to the tumor. In the 1980s, a novel platform for transanal surgery was introduced, known as transanal endoscopic microsurgery (TEM). Since then two additional platforms, transanal endoscopic operation (TEO) and transanal minimally invasive surgery (TAMIS), have also been developed. In each of these three approaches, the rectum is distended by insufflation of carbon dioxide and the tumor is removed under direct endoscopic visualization, using either specially designed or conventional laparoscopic instruments. These platforms allow the removal of tumors located high in the rectum, beyond the reach of the conventional TAE.

The advantages of LE are lower rates of mortality and morbidity, with fewer long-term functional sequelae than radical resection. However, LE is a compromise oncologically because it is associated with a higher risk of LR and does not offer an opportunity to directly examine local nodes. Current National Comprehensive Cancer Network (NCCN) guidelines support the use of LE only in the treatment of carefully selected T1 rectal cancers. The oncologic outcomes for local excision of T2 tumors remain unacceptably high.

Apart from local excision, two methods are used for local destruction of rectal cancer: endocavitary contact radiation (ECR) and electrocautery. Both achieve destruction of the tumor, but neither provides tissue specimens for pathologic examination. ECR has the benefit of being an outpatient procedure and is typically performed with use of a local anesthetic and sedation; electrocoagulation requires induction of general anesthesia and a hospital stay, similar to LE. As TAE rises in popularity, these destructive techniques are falling out of favor. However, ECR may still have a role, especially in the treatment of frail patients.

In this chapter, we will describe local treatment of rectal cancer. We will review patient selection and the techniques and outcomes associated with these approaches. Given the intense focus and research on LE for rectal cancer and its increasing popularity during the past decade, we will preferentially focus on these modalities.

Preoperative Evaluation

Evaluation of all patients diagnosed with rectal cancer should include a full medical history, physical examination, and baseline carcinoembryonic antigen serum level. Digital rectal examination allows direct assessment of the location, size, and fixity of low tumors and their relationship to the sphincter complex.

Although most patients with newly diagnosed rectal cancer have already had a colonoscopy before referral to a surgeon, a proctoscopy should be performed to confirm the location of the tumor. A full colonoscopy should be performed before treatment for patients who have not already had this procedure.

Endorectal ultrasound (ERUS), magnetic resonance imaging (MRI), and computed tomography (CT) are routinely used in the staging of rectal cancer. ERUS is perhaps the most valuable tool in staging early rectal tumors. It provides high-resolution imaging of the different histologic layers of the bowel wall and is excellent for delineating T stage in early-stage rectal cancers. It can also provide short-range information about nodal status and demonstrate involvement of the mesorectum. MRI with use of an endorectal coil also images tumors within the bowel wall very accurately, although the technology is not widely used. Phased-array MRI has rapidly become the gold standard in the preoperative staging of rectal cancer. It provides high-resolution images of the rectum, mesorectum, surrounding pelvic structures, and the muscles of the pelvic floor, in multiple planes. MRI is especially useful in staging advanced tumors, particularly in defining the level of invasion into the mesorectum, nodal status, and the relationship of the tumor to the mesorectal fascia. Unlike ERUS, MRI does not differentiate the T stage of tumors confined to the bowel wall. A CT scan of the chest, abdomen, and pelvis should also be performed to exclude metastatic disease.

The patient’s functional status and baseline bowel function should be assessed before planning surgery. Some patients may not be good candidates for TME because of significant comorbidities, and some may refuse a permanent colostomy. These patients may benefit from transanal LE as a noncurative procedure. In other cases, poor preoperative bowel function and incontinence may diminish some of the benefits of LE, making TME with a permanent stoma the better option.

Initial Selection

The ideal candidate for LE has a superficial, mobile tumor that is localized to the rectal wall (T1). If cure is the aim, there should be no evidence of nodal involvement or distal metastases. Although tumor size itself is not an absolute contraindication to LE, larger tumors are often more advanced and are more likely to have metastasized to the regional lymph nodes. Therefore, LE is not recommended for tumors that encompass greater than 40% of the circumference of the rectal wall or measure more than 4 cm in diameter.

In general, patients with tumors in the distal rectum are the best candidates for LE. These patients are most likely to benefit from LE because TME would require an APR with a permanent colostomy or a coloanal anastomosis. Such tumors are also easier to reach with conventional TAE techniques. However, the new transanal endoscopic platforms allow removal of tumors located in the mid and upper rectum.

Surgical Technique