Prognostic significance of tumor volume in radical prostatectomy and needle biopsy specimens

Purpose: This review addresses the controversies that persist relating to the prognosis and reporting of tumor volume in adenocarcinoma of the prostate.

Materials and methods: A search was performed using the MEDLINE database and referenced lists of relevant studies to obtain articles addressing the quantification of cancer on radical prostatectomy and needle biopsy.

Results: In the 2010 TNM classification system T2 tumor at radical prostatectomy is subdivided into pT2a (unilateral tumor occupying less than ½ a lobe), pT2b (unilateral tumor greater than ½ a lobe) and pT2c (bilateral tumor). This pathological substaging of T2 disease fails on several accounts. In most studies pT2b disease almost does not exist. By the time a tumor is so large that it microscopically occupies more than ½ a lobe, in the majority of cases there is bilateral (pT2c) tumor. An even greater flaw of the substaging system for stage pT2 disease is the lack of prognostic significance. In reporting pathologically organ confined cancer, it should be merely noted as pT2 without further subclassification. The data are conflicting as to the independent prognostic significance of objective measurements of tumor volume in radical prostatectomy specimens. The most likely explanation for the discordant results lies in the strong correlation of tumor volume with other prognostic markers such as extraprostatic extension and positive margins. In studies where it is statistically significant on multivariate analysis, it is unlikely that knowing tumor volume improves prediction of prognosis beyond routinely reported parameters to the degree that it would be clinically useful for an individual patient. An alternative is to record tumor volume as minimal, moderate or extensive, which gives some indication to the urologist as to the extent of disease. Not only does providing an objective measurement not add useful prognostic information beyond what is otherwise routinely reported by the pathologist, but many objective measurements done in routine practice will likely not be an accurate indicator of the true tumor volume. There is also a lack of consensus regarding the best method of measuring tumor length when there are multiple foci in a single core separated by benign intervening prostatic stroma. Some pathologists, this author included, consider discontinuous foci of cancer as if it was 1 uninterrupted focus, the rationale being that these discontinuous foci are undoubtedly the same cancer going in and out of the plane of section. Measuring the cancer from where it starts to where it ends on the core gives the minimal length of cancer in the prostate. Others measure each focus individually, and the sum of these measurements is considered the cancer length on the core. Quantifying cancer with an ocular micrometer to record the total length or percent length of cancer is time-consuming, and the data are conflicting whether this is superior to other, simpler methods and whether any potential differences in predictive accuracy would translate into changes in clinical management. It is recommended that at a minimum the number of positive cores be recorded, unless fragmented involved cores preclude evaluation, along with at least 1 other more detailed measurement such as the percent of core involvement or length of cancer.

Conclusions: Consensus has been reached on some of the issues relating to quantifying tumor volume in prostate cancer, such as the lack of utility of substaging pT2 disease. Other questions such as whether to include or subtract intervening benign prostate tissue on prostate needle cores will require additional studies. Finally, matters such as the need to quantify cancer at radical prostatectomy or which method of quantifying cancer on needle biopsy is superior will likely remain contentious due to the close interrelationship and redundancy of prognostic variables.