Colon and Rectal Cancers: Pathologic Staging and Assessment

A Continuing Medical Education Activity sponsored by InforMEDical Communications, Inc.

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Introduction

In the evaluation and management of an oncology patient, tumor stage is a key reference point. It is also an essential comparator across patients in the clinical and translational research that advances cancer medicine.

Tumor stage refers to the anatomic extent of the disease at the time of discovery, codifying "how much" tumor is present. The concept of stage-related prognosis is straightforward and based on decades of irrefutable data: i.e., the greater the amount of disease at discovery, the lower the likelihood of cure and vice versa. Stage has long been known to be a predictor of ultimate outcome and even today, for the majority of tumor types, remains the most powerful prognostic factor.

The determination of tumor stage is a team effort involving the surgeon, the radiologist, and the pathologist, each of whom contributes directly to the sum of the information needed to accurately determine the extent of the patient's disease.

For the medical oncologist and the radiation oncologist, accurate staging information is essential for optimal patient management and the delivery of quality cancer care. In short, staging involves all of the disciplines involved in multidisciplinary care. The goal of this monograph is to review the key elements of stage determination and reporting for colorectal cancer for surgeons, radiologists, and pathologists and to highlight for the users of pathology reports, such as radiation and medical oncologists, the key prognostic features of pathological assessment of a colorectal resection specimen.

In the last decades, increasing numbers of pathological, serological, and molecular factors have been shown to be associated with survival, response to therapy, or both. In the interest of increasing the prognostic value of stage, which has traditionally referred only to the anatomic extent of disease, non-anatomic factors of these types had begun to be incorporated into stage groupings for some cancers. As a result, the concept of anatomic stage had begun to undergo subtle "mission drift," an issue that recently has been addressed by the American Joint Committee on Cancer (AJCC) and the International Union Against Cancer (UICC). It has been recognized that non-anatomic factors address "what kind of disease" is present rather than "how much" disease is present.

Prognostic power is increased when both anatomic and non-anatomic factors are considered simultaneously, but it is useful to preserve them as separate parameters. Merging them into a stage grouping has the effect of obscuring the relative contribution of each in any given case.

The 7th Edition of the AJCC Staging Manual and the 7th Edition of the UICC TNM Manual both define stage on purely anatomic bases but allow for the inclusion of non-anatomic prognostic factors validated by clinical studies and/or employed in standard patient management into an overall prognostic algorithm.^1-2 The anatomic details that define the TNM categories and the TNM groupings that define stage are updated based on new data sets and published studies. As such, the new stage-prognostic factor algorithms are evidence-based and concordant with evolving oncologic practice. The integrity of anatomic stage, a factor likely always to be important in cancer patient care, is preserved, but incorporation of newer molecular and other non-anatomic prognostic factors is made possible in this framework. In turn, the usefulness and prognostic power of non-anatomic factors that define the biologic type of disease would be expected to increase when considered in the context of stage.

TNM stage, though recommended by professional bodies such as the AJCC, the College of American Pathologists (CAP), the Commission on Cancer (COC) of the American College of Surgeons, and the National Cancer Institute, is not the only staging system for colorectal cancer.^3-7 Historically, several different staging systems for colorectal cancer have been proposed and variously employed. These include the Dukes' system, the Asler-Coller modification of the Dukes' system, and others. Although useful and well-founded in general principle, these systems are neither regularly updated as new data becomes available nor do they have defined rules of interpretation and application that allow for uniform use. The general ground rules of TNM staging and details of the stage category definitions for colorectal cancer are enumerated below. These elements directly contribute to the reproducibility of TNM staging, which in turn, contributes to high-quality patient care and cancer research. Uniform staging criteria applied in a uniform manner are also essential for valid clinical research and accurate evaluation of therapies and outcome.

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