GRADING AND STAGING OF TUMORS

Prognosis of the course of the disease and the determination of efficacy of various forms of cancer treatment require a high degree of similarity among the tumors being considered.

Systems have been developed to express, at least in semiquantitative terms, the level of differentiation, or grade, and extent of spread of a cancer within the patient, or stage, as parameters of the clinical gravity of the disease.

Grading of a cancer is based on the degree of differentiation of the tumor cells and the number of mitoses within the tumor as presumed correlates of the neoplasm's aggressiveness. Thus, cancers are classified as grades I to IV with increasing anaplasia. Criteria for the individual grades vary with each form of neoplasia and so are not detailed here, but all attempt, in essence, to judge the extent to which the tumor cells resemble or fail to resemble their normal counterparts. Although histologic grading is useful, the correlation between histologic appearance and biologic behavior is less than perfect. In recognition of this problem and to avoid spurious quantification, it is common practice to characterize a particular neoplasm in descriptive terms, for example, well-differentiated, mucin-secreting adenocarcinoma of the stomach, or highly undifferentiated, retroperitoneal malignant tumor—probably sarcoma. In general, with a few exceptions, such as soft tissue sarcomas, grading of cancers has proved of less clinical value than has staging.

The staging of cancers is based on the size of the primary lesion, its extent of spread to regional lymph nodes, and the presence or absence of blood-borne metastases. Two major staging systems are currently in use, one developed by the Union Internationale Contre Cancer (UICC) and the other by the American Joint Committee (AJC) on Cancer Staging. The UICC employs a classification called the TNM system—T for primary tumor, N for regional lymph node involvement, and M for metastases. The TNM staging varies for each specific form of cancer, but there are general principles. With increasing size, the primary lesion is characterized as T1 to T4. T0 is added to indicate an in situ lesion. N0 would mean no nodal involvement, whereas N1 to N3 would denote involvement of an increasing number and range of nodes. M0 signifies no distant metastases, whereas M1 or sometimes M2 indicates the presence of blood-borne metastases and some judgment as to their number.

The AJC employs a somewhat different nomenclature and divides all cancers into stages 0 to IV, incorporating within each of these stages the size of the primary lesions as well as the presence of nodal spread and distant metastases. The staging systems and additional details are mentioned in appropriate chapters, in conjunction with the discussion of specific tumors. It merits emphasis here, however, that staging of neoplastic disease has assumed great importance in the selection of the best form of therapy for the patient. It bears repeating that staging has proved to be of greater clinical value than grading. In some cases, such as for lung cancers, staging has been greatly aided by imaging techniques such as positron emission tomography.[55]

Date: 2016-04-22; view: 761