PERSPECTIVE, PATTERNS OF SPREAD, AND PATHOLOGY
The rectum is the most common site for intestinal cancer, with 40,000 cases annually, equally divided by gender.
PERSPECTIVE AND PATTERN OF SPREAD
Rectal cancers present according to the early warning signs of change in bowel habits, bleeding into stools, and narrowing or pencil stools. However, such signs are not in keeping with early detection. Rectal cancers should be uncovered in their asymptomatic stage during annually performed rectal examinations and testing for hemoccult blood in the stool. The rectum is perhaps the most common site for intestinal cancer, with 40,000 cases annually, equally divided by gender. Fortunately, the vast majority of cases are controlled, and patients become cancer survivors, often with rectal sphincter preservation. More than 90% of patients become 5-year survivors, and mortality rates have been trending downward, more dramatically in females than males. The histopathology of rectal cancers is mainly adenocarcinoma, and the staging system is not applicable to lymphomas or sarcomas. Cancer spread patterns are both intraperitoneal and extraperitoneal because of its pelvic location (Fig. 32.2; Table 32.2).
The sagittal section is best to illustrate differences in males and females. Figure 32.2A-B correlates with SIMLAP Table 32.2A-B.
• Rectal lesions often present with rectal bleeding (65% to 90%), change in bowel habits (45% to 80%), and diminished stool caliber. Pain and tenesmus may occur as later symptoms. Rectal bleeding is often initially ascribed to hemorrhoids, and the lesions may go uninvestigated for long periods of time, especially in patients 40 years of age or younger. Most rectal cancers can be detected and their mobility defined by a digital rectal examination (65% t 80%). Proctosigmoidoscopy should then be performed with appropriate biopsies to establish the diagnosis.
• Rectal digital examination should be a part of every physical examination on patients older than age 40 years regardless of symptoms or physical condition. If a lesion is found, the inferior extent should be noted (relative to anal verge and coccyx), as well as its location (anterior, posterior, left, right), degree of circumference involved, and degree of mobility (mobile, tethered, fixed)
PATHOLOGY
The histopathology of rectal cancers are mainly adenocarcinomas, and the staging system is not applicable to lymphomas or sarcomas (Table 32.1; Fig. 32.1).
Figure 32.1 | Adenocarcinoma. Microscopically, this colon adenocarcinoma consists of moderately differentiated glands with a prominent cribriform pattern and frequent central necrosis.
Figure 32.2 | Patterns of spread and T categories. A. Male. B. Female. The patterns of spread and the primary tumor classification are similarly color coded: Tis (cancer in situ of mucosa), yellow; T1 (infiltrates the submucosa), green; T2 (penetrates t e muscularis externa), blue; T3 (reaches the subserosa), purple; and T4 (invades through the serosa into a neighboring viscera), red. The concept of visualizing patterns of spread to appreciate the surrounding anatomy is well demonstrated by the six-directional pattern, i.e., SIMLAP Table 32.2.
TNM STAGING CRITERIA
TNM STAGING CRITERIA
The staging of rectal cancer is relatively unchanged and based on the depth of penetration of its wall and whether lymph nodes are involved. Because the rectum lies in the sacral hollow, it has no peritoneum on its lateral or posterior surfaces with direct access to the sacral plexus of nerves. The rectum has been variously defined anatomically because only for half of its length i it an extraperitoneal organ. Its relationship to genitourinary organs differs in the male and female pelvis (Fig. 32.2). The cancer invades the mucosa (T1), muscularis (T2), and serosa (T3) anteriorly; however, posteriorly it has no barrier to invasion of the sacral hollows. Perineural invasion of the sacral plexus is T4.
Generally, there is no overarching principle or context design for the digestive system (gastrointestinal tract) or major digestive glands (MDGs). Stages are frequently expanded to six by subdividing stages into A and B. The T and N categories are assigned to a stage grouping, specifically for division of stage into more (a) versus less (b) favorable groupings. This occurs at different stages for different sites.
This site has a clear separation of T progression I/II from N progression III/IV. Stages IIIA and IIIB show node progression, and stage IIIC shows venous invasion (V1); stage IV is metastatic. Because this site is the dominant cancer, this staging system impacts on other gastrointestinal sites and major digestive gland sites.
SUMMARY OF CHANGES SEVENTH EDITION AJCC
• In the sixth edition, Stage II was subdivided into IIA and IIB on the basis of whether the primary tumor was T3N0 or T4N0, respectively, and Stage III was subdivided into IIIa (T1-2N1M0), IIIB (T3-4N1M0), or IIIC (any TN2M0). In the seventh edition, further substaging of Stage II and III has been accomplished, based on survival and relapse data that was not available for the prior edition (Fig. 32.3).
• Expanded data sets have shown differential prognosis within T4 lesions based on extent of disease. Accordingly T4 lesions are subdivided as T4a (tumor penetrates the surface of the visceral peritoneum) and as T4b (tumor directly invades or is histologically adherent to other organs or structures).
• The potential importance of satellite tumor deposits is now defined by the new site-specific factor tumor deposi (TD) that describes their texture and number. T1-2 lesions that lack regional lymph node metastasis but have tumor deposit(s) will be classified in addition as N1c
• The number of nodes involved with metastasis influence prognosis within both N1 and N2 groups. Accordingly N1 will be subdivided as N1a (metastasis in 1 regional node) and N1b (metastasis in 2–3 nodes), and N2 will be subdivided as N2a (metastasis in 4–6 nodes) and N2b (metastasis in 7 or more nodes).
• Stage Group II is subdivided into IIA (T3N0), IIB (T4aN0), and IIC (T4bN0).
• Stage Group III:
• A category of N1 lesions, T4bN1, that was formerly classified as IIIB was found to have outcomes more akin to IIIC and has been reclassified from IIIB to IIIC
• Similarly, several categories of N2 lesions formerly classified as IIIC have outcomes more akin to other stage groups; therefore, T1N2a has been reclassified a IIIA and T1N2b, T2N2a-b, and T3N2a have all been reclassified as IIIB
• M1 has been subdivided into M1a for single metastatic site vs. M1b for multiple metastatic sites.
The TNM Staging Matrix is color coded for identification o Stage Group once T and N stages are determined (Table 32.3).
RECTUM
Figure 32.3 | TNM staging diagram presents a vertical arrangement with color bars encompassing TN combinations showing progression. Rectal cancers can be resected as stage II A/B (purple) with N1 nodes, but are less favorable and borderline resectable as stage IIIC (red) as N2 nodes (>4) are found; stage IV is (black) metastatic. Stage 0, yellow; I, green; II, blue; III, purple; IV, red; and IV (metastatic), black. Definitions of TN on left and stage grouping on right
T-ONCOANATOMY
ORIENTATION OF THREE-PLANAR ONCOANATOMY
The three-planar anatomic isocenter for the rectum occupies the sacral hollow (S1–S5) inside the true pelvis, retropubically located from an anterior view (Fig. 32.4).
T-oncoanatomy
The T-oncoanatomy is displayed in three planar views. A. Coronal, B. Sagittal, C. Transverse axial. (Fig. 32.5 Male [A,B,C]; Female [A,D,E]).
The rectum, about 12 cm long, extends from a point opposite the third sacral vertebra down to the apex of the prostate in the male and to the apex of the perineal body in the female, that is, to a point 4 cm anterior to the tip of the coccyx. It may be arbitrarily defined as the distal 10 cm of the large intestine as measured by preoperative sigmoidoscopy from the anal verge (Fig. 32.4).
• Coronal: The rectum extends approximately 10 to 12 cm; the retrosigmoid area is 10 to 15 cm from this junction. The rectum has no epiploic appendages, no haustrations, and no teniae. It is covered by peritoneum in front and on both sides in its upper third and on the anterior wall only in its middle third; there is no peritoneal covering in the lower third.
• Sagittal: In the lower rectum, the mucosa is thrown into longitudinal folds, known as the rectal columns or the columns of Morgagni. Between them, just above the white line of Hilton, are the anal pits or sinuses. About 4 cm long, the anal canal courses downward and backward from the apex of the prostate or the perineal body. The anocutaneous line (pectinate line), or white line of Hilton, at the base of the rectal columns, marks the site of the original anal membrane that separated the endodermal gut from the ectodermal proctoderm. The transition from colon to rectum has been explicitly defined by the American Joint Committee o Cancer as marked by the fusion of the tenia of the sigmoid colon to the circumferential longitudinal muscle of the rectum. This occurs 12 to 15 cm from the dentate line. The upper third is covered anteriorly and at its sides by peritoneum, which is completely absent in its lower third.
• Transverse: The rectouterine cul-de-sac (pouch of Douglas) in females is the rectovesical pouch in males and inferiorly becomes the Denonvilliers fascia, separating and shielding the rectum from direct prostate cancer invasion. The rectal mucosa is smooth and is characterized by transverse folds, the valves of Houston that divide the rectum into thirds. In the three-dimensional three-planar views of the male (Fig. 32.5B,C) and female (Fig. 32.5D,E) pelvises, the axial views are most informative. Comparison of the location of the female cervix with the male prostate and their critical relationship to the rectum and bladder presents a specific challenge t radiation oncologists to avoid injuring this important organ.
Figure 32.4 | Orientation and overview of oncoanatomy. The three-planar anatomic isocenter for the rectum occupies the sacral hollow (S1–S5) inside the true pelvis, retropubically located from an anterior view. A. Coronal. B.Sagittal.
Figure 32.5 | T-oncoanatomy. Connecting the dots. Structures are color coded for cancer stage progression. The color code for the anatomic sites correlates with the color code for the stage group (Fig. 32.3) and patterns of spread (Fig. 32.2) and SIMLAP table (Table 32.2). Connecting the dots in similar colors will provide an appreciation for the 3D oncoanatomy.
N-ONCOANATOMY AND M-ONCOANATOMY
N-ONCOANATOMY
The nodal drainage and distribution follow its blood supply, which is complicated because of its anatomy as both a pelvic and an abdominal organ. The superior third follows the superior rectal lymph nodes, which follow the inferior mesenteric node to the portal and caval nodes. The middle portion drains directly into the pelvic internal iliac nodes. The lower third drains into inguinal lymph nodes (Fig. 32.6A; Table 32.4).
Regional Lymph Nodes
Regional lymph nodes are located (i) along the course of the major vessels supplying the colon and rectum, (ii) along the vascular arcades of the marginal artery, and (iii) adjacent to the colon, that is, located along the mesocolic border of the colon. Specificall, the regional lymph nodes are the pericolic and perirectal nodes and those found along the ileocolic, right colic, middle colic, left colic, inferior mesenteric artery, superior rectal (hemorrhoidal), and internal iliac arteries.
In the assessment of pN, the number of lymph nodes sampled should be recorded. The number of nodes examined from an operative specimen has been reported to be associated with improved survival, possibly because of increased accuracy in staging. It is important to obtain at least 10 to 14 lymph nodes in radical colon and rectum resections in patients without neoadjuvant therapy, but in cases in which tumor is resected for palliation in patients who have received preoperative radiation, fewer lymph nodes may be removed or present. In all cases, however, it is essential that the total number of regional lymph nodes recovered from the resection specimen be described since that number is prognostically important. A pN0 determination is assigned when these nodes are histologically negative, even though fewer than the recommended number of nodes has been analyzed. However, when fewer than the number of nodes recommended by the College of American Pathologists have been found, it is important that pathologists report the degree of diligence of their efforts to find the lymph nodes in the specimen
The regional lymph nodes for each segment of the large bowel are listed in Table 32.4.*
M-ONCOANATOMY
The venous drainage is different for each third of the rectum owing to its anatomic position as an abdominal and pelvic organ. Superiorly, the superior rectal vein drains into the inferior mesenteric vein and then portal vein, resulting in a high probability of liver metastases. The middle and inferior thirds drain into the internal and external iliac veins and the inferior vena cava and then to the right side of the heart and into lung. The middle rectal vein may predispose to osseous pelvic metastases because of anastomoses of perirectal veins with intervertebral veins (see Fig. 32.6B).
*Preceding passage from Edge SB, Byrd DR, Compton CC, et al., AJCC Cancer Staging Manual, 7th edition. New York, Springer, 2010, pp. 145–146.
Figure 32.6 | A. N-oncoanatomy. Sentinel nodes of the rectum include the pelvic perirectal and sacral nodes. B. M-oncoanatomy.
STAGING WORKUP
RULES OF CLASSIFICATION AND STAGING
Clinical Staging and Imaging
Extension of diagnostic imaging to staging is gaining in popularity. Virtual colonoscopy and sigmoidoscopy are challenging endoscopic colonoscopy as to accuracy in diagnosing adenocarcinomas. Endoscopic ultrasound shows the layers of the colon and rectal wall and their penetration by cancer. Endorectal magnetic resonance imaging (MRI) is most valuable to demonstrate extracolonic and extrarectal invasion into adjacent structures. Computed tomography (CT) is preferred for detecting liver and lung metastases (Table 32.5).
Pathologic Staging
The surgically resected rectum and associated lymph nodes removed are assessed. Tumor extension and location of both primary and nodes should be documented. Accurate radial margins should be marked and recorded and are defined “a the surgically dissected surface adjacent to the deepest point of tumor invasion beyond the wall of the rectum.” The completeness of resection depends on the clearing of the deepest point of invasion: R0, complete; R1, microscopic; and R2, macroscopic.
Oncoimaging Annotations
• Although colonoscopy is more accurate in assessment for small polyps, overall cost effectiveness is greater when double-contrast barium enema examinations are used.
• CT colonography is a recent addition to the modalities used to screen for colorectal cancer and polyps. This modality requires further refinement and testing before being mor widely adopted.
• Transrectal ultrasonography and MRI are able to demonstrate the extent of tumor through the rectal wall and provide some assessment for lymphadenopathy.
• If there is clinical suspicion of metastasis or elevated carcinoembryonic antigen level, CT and MRI are useful for determining the presence and site of recurrent disease. Overall accuracy for the detection of recurrent disease with these modalities is 90% to 95%. This evaluation may require fine needle aspiration biopsy under direct CT guidance.
• Other noninvasive means to determine the presence or absence of recurrent or metastatic tumor are nuclear medicine scanning techniques with radiolabeled monoclonal antibodies and positron emission tomography techniques using fluo rodeoxyglucose. Some of these have shown great potential.
PROGNOSIS AND CANCER SURVIVAL
PROGNOSIS
The limited number of prognostic factors are listed in Table 32.6.
CANCER STATISTICS AND SURVIVAL
The digestive system, or gastrointestinal tract, which includes MDGs, accounts for 275,000 new patients annually, with colon and rectum responsible for >50%, or about 140,000 new diagnoses annually. Approximately half of these patients eventually die of these cancers. MDG cancers as a group are more lethal; only a handful of patients become long-term survivors. Fortunately, colon and rectal cancers are the most common, with the majority of patients becoming 5-year survivors (63%) responding to chemoradiation programs, often with the sparing of the rectal sphincter with conservative surgery. Anal cancers are the most responsive to chemoradiation (5-fluorouracil and cisplatin), eliminating the need for surgery. The 5-year survival rate is >90%, with anal sphincter preservation. This regimen has been proven to be very effective in clinical trials and to result in more long-term survivors, which is currently reflected in the literature. Live, bile duct, and pancreatic cancers are among the poorest in terms of survival, which is often measured in months rather than years.
The rectum accounted for approximately 39,670 new cancer cases, with a 5-year survival rate improvement over the last five decades of 23%. Currently, relative 5-year survival for all stages is 62.3%, but, when localized, it improves to 90.1% (see Table 23.8). Local recurrence is highly dependent on site in the rectum, that is, 18% overall for tumors >7 cm from the anal verge. Stage is a strong prognosticator for local recurrence, that is, T1, T2 38% and T3, T4 30%, but with positive node failure it doubles to 65% (Fig. 32.8).
Note the anachronism of Stage IIIA equalling Stage I ≤ 74% 5 year survival. Stage IIIA is similar T1, T2 but N1c are tumor deposits in subserosa or mesentery without lymph node involvement. More often N1a and N1b have one or 2 to 3 nodes associated with T3, T4 primaries.
Figure 32.7 | Axial CTs of S1 and S3 level correlate with the T-oncoanatomy transverse section. Oncoimaging with CT is commonly applied to staging cancers, often combined with PET to determine true extent of primary cancer and involved lymph nodes. A. Female (correlates with Fig. 32.5E). 1. Left ovary. 2. Physiologic free fluid 3. Uterus (endometrial cavity (normal in menstruating-age females). 4. Iliopsoas muscle. 5. Rectum. 6. Round ligament of uterus. UB, urinary bladder. B. Male (correlates with Fig. 32.5C). 1. Sigmoid colon. 2. Iliopsoas muscle. 3. Rectus abdominus muscle. 4. Obturator internus muscle. 5. Acetabular roof.
Figure 32.8 | Five-year observed survival adenocarcinoma of the rectum. (Data from Edge SB, Byrd DR, Compton CC, et al. AJCC Cancer Staging Manual, 7th ed. New York: Springer, 2010, p. 154.)