Manual for Staging of Cancer; Fifth Edition; Edited by Irvin D. Fleming, M.D., Jay S. Cooper, M.D., Donald Earl Henson, M.D., Robert V.P. Hutter, M.D., B.J. Kennedy, M.D., Gerald Murphy, M.D., D.S.c., Brian O'Sullivan, M.B., F.R.C.P.C., F.R.C.P.I., Leslie H. Sobin, M.D., John W. Yarbro, M.D., Ph.D.; Copyright 1997, the American Joint Committee on Cancer. Published by Lippincott-Raven Publishers. Chapter 12, pp. 83 - 90.

The TNM classification for carcinomas of the colon and rectum provides more detail than other staging systems. Compatible with Dukes, the TNM adds greater precision in the identification of prognostic subgroups. The TNM is based on the depth of tumor invasion into the wall of the intestine, extension to adjacent structures, the number of regional lymph nodes involved, and the presence or absence of distant metastasis. The TNM classification applies to both clinical and pathologic staging. Most cancers of the colon or rectum, however, are staged after pathologic examination of the resected specimen. This staging system applies to all carcinomas arising in the colon, rectum, or in the vermiform appendix.

ANATOMY

Divisions of the Colon and Rectum:

Cecum
Ascending colon
Hepatic flexure
Transverse colon
Splenic flexure
Descending colon
Sigmoid colon
Rectosigmoid junction
Rectum

Cancers that occur in the anal canal are staged according to the classification used for the anus (see Chapter 13).

Primary Site. The large intestine (colorectum) extends from the terminal ileum to the anal canal. Excluding the rectum and vermiform appendix, the colon is divided into four parts: the right or ascending colon, the middle or transverse colon, the left or descending colon, and the sigmoid colon. The sigmoid is continuous with the rectum which terminates at the anal canal.

The cecum is a large pouch that forms the proximal segment of the right colon. It usually measures 6 cm by 9 cm and is covered with peritoneum. The ascending colon measures 15 to 20 cm in length and is located retroperitoneally. Connecting the ascending colon to the transverse colon is the hepatic flexure which lies under the right lobe of the liver near the duodenum.

The transverse colon lies more anteriorly than the other divisions of the colon. It is supported by the transverse mesocolon which is attached to the pancreas. Anteriorly, its serosa is continuous with the gastrocolic ligament. The transverse colon is connected to the descending colon by the splenic flexure which is located near the spleen and tail of the pancreas. The descending colon, which measures 10 to 15 cm in length, is also located retroperitoneally. The descending colon becomes the sigmoid at the origin of the mesosigmoid. The sigmoid loop extends from the medial border of the left posterior major psoas muscle to the rectum, which begins at the termination of the mesosigmoid.

Approximately 12 cm in length, the rectum extends from the third sacral vertebra to the apex of the prostate gland 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 is often defined as the distal 10 cm of the large intestine as measured from the anal verge with a sigmoidoscope. The rectosigmoid segment is usually 10 to 15 cm from the anal mucocutaneous junction. The rectum is covered by peritoneum in front and on both sides in its upper third and only on the anterior wall in its middle third. The peritoneum is reflected laterally from the rectum to form the perirectal fossa and anteriorly the uterine or rectovesical fold. There is no peritoneal covering in the lower third, which is often known as the rectal ampulla. The anal canal, which measures 4 to 5 cm in length, courses downward and backward from the apex of the prostate gland or from the perineal body to the anal verge. (See Fig. 12-1.)

(Total length of large intestine approximately 150 cm). * The rectosigmoid is of anatomic and surgical importance because of the blood supply and the disappearance of the mesosigmoid. While the rectosigmoid is truly a junction, some authors include 1 inch of the sigmoid above and 1 inch of rectum below and refer to it as the rectosigmoid region. These measurements are APPROXIMATIONS ONLY. Each person is different and these measurements should be used as GUIDELINES ONLY. FIG. 12-1. The anatomic areas of the colon and rectum are: cecum (1); ascending colon (2); hepatic flexure (3); transverse colon (4); splenic fixture (5); descending colon (6); sigmoid (7); rectosigmoid (7.5); rectum (8); anal canal (9);.

Regional Lymph Nodes. Regional nodes are located: (1) along the course of the major vessels supplying the colon and rectum; (2) along the vascular arcades of the marginal artery; and (3) adjacent to the colon; that is, located along the mesocolic border of the colon. Specifically, 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.

For pN, the number of lymph nodes sampled should be recorded. It is desirable to obtain at least 12 lymph nodes in radical colon resections; however, in cases in which tumor is resected for palliation or in patients who have received pre-operative radiation, only a few lymph nodes may be present.

The regional lymph nodes for each segment of the colon are:

Metastatic Sites. Although carcinomas of the colon and rectum can metastasize to almost any organ, the liver and lungs are the most common sites. Seeding of other segments of the colon or small intestine can also occur.

RULES FOR CLASSIFICATION

Clinical Staging. Clinical assessment is based on medical history, physical examination, routine and special imaging procedures, sigmoidoscopy, colonoscopy with biopsy, and special examinations designed to demonstrate the presence of extracolonic metastasis, for example, chest films, liver function tests, and liver scans.

Pathologic Staging. Colorectal cancers are usually staged after pathologic examination of the resected specimen and surgical exploration of the abdomen. The definition of in situ carcinoma pTis includes cancer cells confined within the glandular basement membrane (intraepithelial) or lamina propria (intramucosal) with no extension through the muscularis mucosae into the submucosa. This definition of pTis is different from that used for the other divisions of the gastrointestinal tract. Neither intraepithelial nor intramucosal carcinomas of the large intestine have a significant potential for metastasis.

Tumor that invades the stalk of a polyp is classified according to the pT definitions adopted for colorectal carcinomas. For instance, tumor that is limited to the lamina propria is listed as pTis, whereas tumor that has invaded the muscularis mucosae and entered the submucosa of the stalk is classified T1.

Lymph nodes are classified N1 or N2 according to the number involved with metastatic tumor. Involvement of 1 to 3 nodes is N1.

Patients with tumor located on the serosal surface as a result of direct extension through the colon are assigned T4. Seeding of abdominal organs, for instance, the distal ileum from a carcinoma of the transverse colon, is considered discontinuous metastasis and should be recorded as M1. Metastatic nodules or foci found in the pericolic or perirectal fat or in adjacent mesentery (mesocolic fat) without evidence of residual lymph node tissue are equivalent to regional lymph node metastasis. Multiple metastatic foci seen microscopically only in the pericolic fat should be considered as metastasis in a single lymph node for classification. A tumor nodule greater than 3 mm in diameter in the perirectal or pericolic fat without histologic evidence of a residual node in the nodule is classified as regional perirectal or pericolic lymph node metastasis. However, a tumor nodule 3 mm or less in diameter is classified in the T category as a discontinuous extension, that is T3.

Metastasis in the external iliac or common iliac lymph nodes is classified M1.

If the tumor recurs at the site of surgery, it is anatomically assigned to the proximal segment of the anastomosis.

DEFINITION OF TNM

*Note: Tis includes cancer cells confined within the glandular basement membrane (intraepithelial) or lamina propria (intramucosal) with no extension through the muscularis mucosae into the submucosa.

**Note: Direct invasion in T4 includes invasion of other segments of the colorectum by way of the serosa; for example, invasion of the sigmoid colon by a carcinoma of the cecum.

STAGE GROUPING

*Dukes B is a composite of better (T3 N0 M0) and worse (T4 N0 M0) prognostic groups, as is Dukes C (Any T N1 M0 and Any T N2 M0)

HISTOPATHOLOGIC TYPE

Adenocarcinoma in situ*
Adenocarcinoma Mucinous carcinoma, (colloid type) (greater than 50% mucinous carcinoma)
Signet ring cell carcinoma (greater than 50% signet ring cell)
Squamous cell (epidermoid) carcinoma Adenosquamous carcinoma
Small cell carcinoma
Undifferentiated carcinoma
Carcinoma, NOS

*The terms "high grade dysplasia" or "severe dysplasia" may be used as synonyms for in situ adenocarcinoma or in situ carcinoma. These cases should be assigned pTis.

HISTOLOGIC GRADE (G)

PROGNOSTIC FACTORS

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