Cancer staging systems are intended to assist clinicians to categorize patients diagnosed with a particular malignancy in terms of their life expectancy and potential response to specific therapeutic strategies. Generally speaking, patients categorized as early stage have anatomically localized malignancy associated with a longer life expectancy and better response particularly to local therapies directed at the primary tumor mass. Late-stage patients are presumed to have metastatic disease indirectly disseminated to distant anatomic sites, associated with shorter life expectancy and requiring systemic therapeutic approaches. A staging system is a set of criteria that defines such categories for a specific malignancy. Stage categories are defined in anatomic terms: How large is the tumor and what anatomic structures have become involved with (i.e., contain invasive proliferations of) tumor cells?
Tumor stage may be used as an eligibility or stratification factor for clinical trials, as a component of algorithms for determining prognosis, and in predicting the efficacy of particular therapeutic strategies for individual patients. Thus, stage serves as an important element of risk–benefit discussions between cancer patients and clinicians. In the context of an aggressive and rapidly fatal malignancy, such as malignant pleural mesothelioma (MPM), these issues are critical to clinical, patient, and caregiver decision-making in relation to balancing expected quantity and quality of life. The practical value of any staging system is measured by its ability to separate patients into categories associated with differing expectations in terms of symptom relief, side effects, freedom from disease progression, and/or survival duration in relation to available treatment strategies.
Staging categorizes the physical extent of tumor growth relative to a patient’s normal anatomy. Categorical labels typically ranging from stage I to stage IV reflect the progressive nature of the underlying biologic process. Corresponding qualitative descriptions of “local” (stage I), “regional” (stages II–III), and “distant” (stage IV) disease refer, respectively, to a tumor that remains confined to the tissue or organ within which it initially arose, one that extends beyond the initiating tissue or organ either by direct growth to immediately surrounding tissues or by microscopic dissemination via lymphatic vessels to draining lymph nodes, and one that is disseminated via the systemic circulation to establish metastases in remote anatomic locations. For some systems, stage categories are defined directly by lists of criteria. However, the recognition that direct extension of the primary mass and metastasis via lymphatic and systemic routes represent separate and mutually independent classification parameters that may be combined to optimally define stage led to the development and preferential use of the more nuanced tumor-node-metastasis (TNM) classification systems.
Definitive determination of stage requires microscopic evaluation of representative tissue samples from the defining anatomic structures. Accurate staging is therefore only possible when all primary tumors have been surgically resected with an adequate margin, relevant regional lymph nodes and any suspected metastases have been biopsied, and the specimens have been subjected to complete gross and microscopic pathologic examination. The resulting classification ...