Staging

The preferred staging system for rectal cancer is the TNM staging system proposed by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC) . This system consists of three categories: 1) tumor (T), which denotes the depth of mural invasion; 2) nodal involvement (N), and 3) distant metastasis (M) (Table 1). The combination of these categories based on clinical and/or pathologic data dictates the stage (Table 2), together providing the best correlation for the patient’s overall prognosis.

Table 1. AJCC TNM Staging Definitions for Rectal Cancer

Used with permission of the American College of Surgeons, Chicago, Illinois. The original source for this information is the AJCC Cancer Staging System.

Table 2. AJCC Prognostic Stage Groupings for Rectal Cancer

Used with permission of the American College of Surgeons, Chicago, Illinois. The original source for this information is the AJCC Cancer Staging System.

A key feature of rectal cancer staging is the importance of clinical stage in determining treatment recommendations. The clinical TNM classification (cTNM) is assigned during initial evaluation of the patient using a combination of endoscopic (proctoscopy, flexible sigmoidoscopy, colonoscopy) and rectal cancer protocol magnetic resonance imaging (MRI) scans to assess tumor presence and penetration of the rectal wall; presence of mesorectal lymph nodes; and computed tomography (CT) of chest, abdomen, and pelvis to determine the presence of distant metastases.Pathologic stage is known only after surgery and may be lower than the clinical stage, because of downstaging caused by neoadjuvant therapy. Also, because micrometastases can be found after pathological evaluation, upstaging is a possibility. The symbol “p” refers to the pathologic version of the TNM classification and is based on gross and histologic examination of endoscopic or surgical specimens. Pathological primary tumor (pT) staging requires examination of the primary resected cancer specimen to assess the depth of mural invasion; pathological node (pN) staging requires resection or biopsy of nodal tissue; and pM requires histologic examination of lesions in distant organs.

Modifiers to TNM classifications do not affect the stage grouping, but they can alert physicians to clinical features important to assessing cancer stage. The “y” prefix indicates specimens assessed during or following neoadjuvant therapy; the cTNM or pTNM category is thus modified by a “y” prefix. The “r” prefix represents a recurrent tumor when staged after a documented disease-free interval. The “m” suffix refers to the presence of multiple primary tumors in a single specimen and is recorded in parentheses, as, for example, in pT(m)NM.

Pathologic analysis of the proctectomy specimen provides the basis for the pathologic stage. The College of American Pathologists (CAP) has provided a list of minimum reporting for each rectal cancer resection specimen that extends beyond the TNM stage of the tumor. Further, it is the responsibility of the pathologist to grade the quality of the mesorectal excision; this grade is an important surrogate for the measure of the quality of surgical resection.