Prognostic Factor Definition

Objective prognostic factors such as age, gender, height, weight, or biologic data can be estimated and their measure is generally not subjected to discussion. Automatic or validated instruments when available are very helpful. In biologic data measurement, knowledge of normal values according to either age or gender is required. However, nonobjective factors are more frequent than objective ones in the clinical research area. Histologic subtype and tumor bulk among many others can be selected as examples.

Assessment of histologic subtype depends on the experience of the pathologist and classification used. When a central review is organized involving senior experienced pathologists, very few discrepancies are noticed between diagnoses for a given case as well as few variations are observed in the distribution of various subtypes with time, i.e., within cohort of patients or studies. However, even when a central review exists, the prognostic value of pathology per se is controversial especially since the use of modern combined-modality therapy.

Tumor bulk is a recognized prognostic factor in Hodgkin's lymphoma. The way used in its evaluation, however, can very much influence the result. The Ann Arbor classification considers the number of lymph node regions involved, and their definition may vary from one study to the other. Some investigators include lung hillar nodes in the mediastinum, while others do not. In estimating mediastinal bulk, two ways of calculation have been proposed that provide different estimations.16 36 Specht and colleagues have tried to precisely measure tumor burden and have demonstrated its prognostic value in early as well as advanced stages disease.37-39 They used both the number of involved regions and the tumor size in each region. This approach may, however, be much difficult to apply in daily practice and sensitive to clinician attention. A more direct method of estimation of tumor burden was assessed by Gobbi and colleagues.40 It consists of using images of the lesions obtained through computed tomography for all deep sites of involvement and those obtained by ultrasonography for superficial lesions. The sum of the volumes of the lesions is used as an estimation of the absolute tumor burden. Its ratio to the patient's body surface area represents the relative tumor burden. The latter parameter was demonstrated to be the most prognostic among all classical factors tested. Again, this approach depends highly on the radiologists' experience and their attention paid in measuring the volume of the lesions.

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