By: Dan Sperling, MD

A European team led by Dr. Karl Engelhard (Martha-Maria Hospital, Nuremberg, Germany) recently published a study on the ability of multiparametric MRI (mpMRI) to detect an index lesion, and characterize its level of disease aggression.[i]

The purpose of the research was to evaluate how accurate mpMRI is for identifying the largest prostate tumor (which is defined as the index lesion, or the tumor most likely to harbor potentially dangerous prostate cancer). Furthermore, the team wanted to know how well such imaging could yield important information about the nature of the tumor.

A total of 55 patients were enrolled in the study. Each patient underwent standard TRUS biopsy to diagnose cancer. After allowing time for blood artifacts to heal, each patient had mpMRI at 1.5 T (T or Tesla refers to the strength of the magnet used for the scan). Based on independent reading, the maximum tumor diameter was determined (assumed to be the index lesion) and its pathology stage was assigned a rating. In all cases, the patients then had radical prostatectomy. The surgically removed glands were analyzed for the presence and nature of any prostate cancer tumors. The mpMRI had detected 55 cancer foci among the 31 patients. Surgical removal revealed 158 cancer foci.

The results of mpMRI’s ability to detect and characterize the index lesions in all 31 patients were as follows:

The authors noted three positive correlations:

1. The maximum tumor diameter of the index lesion identified by MRI correlated with the same dimension on the lab results after surgery (pathology)
2. The volume of the index tumor assessed by MRI correlated with the volume at pathology
3. The pathologic stage of the tumor as characterized by MRI correlated with the stage at pathology.

The study concluded that mpMRI is accurate in detecting the index lesion and estimating the tumor volume and pathologic stage of localized prostate cancer.

This research has important ramifications for treatment planning, especially given the margin of error of standard TRUS biopsy. As an ever-growing trend toward early detection exists, more patients may be qualified for either surveillance with image monitoring (fewer biopsies) or for a focal treatment approach as a middle ground between no treatment vs. radical treatment. Too much uncertainty about the size, shape, location and true degree of aggression attends the results of a conventional 12-core biopsy, due to its random nature. The tendency to overtreat prostate cancer subjects men to the chance of short- and long-term urinary and sexual morbidities (side effects). On the other hand, recommending surveillance for men who may be harboring an aggressive cell line missed by biopsy constitutes the risk of missing a treatment window.

With the ability of mpMRI to identify and monitor an index lesion and provide important information about its likely level of aggression, those patients who are candidates for a minimalist approach to managing their cancer can be comfortable with and confident in their treatment choice.