When prostates removed surgically for prostate cancer are examined, 50-75% of these specimens contain more than one area or focus of cancer and called multifocal prostate cancer. In other words, only about 25% of men may have a unifocal prostate cancer lesion that may be suitable for focal therapy. In these prostates with multifocal cancer, however, the gland has on average 3-5 tumors in various stages of evolution.
One of these cancerous areas is commonly bigger in volume than the others and called the index lesion.
In attempting to sort out when a focus of prostate cancer becomes significant and needing treatment, there is some acceptance that an index lesion with a Gleason score of 6 or more and with a volume of >0.5 cm3 is a size where treatment may become necessary.
Smaller index tumor volumes,or, smaller total tumor volumes as in those with multifocal disease can probably forgo treatment but diligently followed through active surveillance (AS).
During AS, PSA velocity (PSAV) monitoring can be valuable and a PSAV greater than 0.75ng/ml/year is associated significantly with prostate cancer and possibly progression. On the other hand, a PSA density of 0.08ng/ml/cc at first re-biopsy is a significant predictor of prostate cancer progression and probable need for treatment. However, no tumor marker is definitive and only a needle biopsy of the prostate can definitively diagnose prostate cancer, assess Gleason score and suggest progression of the cancer.
For the significant index lesion then, what is a tumor volume demanding treatment? Do we consider focal treatment of just that index lesion (focal ablation) with a minimally invasive treatment option such as HIFU, cryo or laser and disregard the other smaller satellite lesions in a multifocal prostate cancer?
Prostate cancer has a very varied biological potential and the clinical and prognostic significance of these smaller satellite lesions in men with multifocal prostate cancer is unknown.
Some have suggested that prostate cancer spread or metastasis, probably originates from a precursor cell and that the precursor cell may arise from the index lesion and therefore maybe treating only the index lesion is necessary. In this manner, by focusing treatment on only the index lesion, we may reduce the risk of collateral damage, a common byproduct of robotic prostatectomy and radiation and so preserve a man’s quality of life (QOL).
However, the desire for focal ablation or treatment of just the index lesion in those with multifocal disease needs to be tempered somewhat because of a number of concerns, least of which is the issue that men with higher tumor volumes have a greater risk for recurrence after treatment. Furthermore, prostate cancer located in the peripheral zone of the prostate (about 70% of prostate cancers are located in this zone) in contrast to those located in the transitional and central zones of the prostate, have a greater ability for prostate capsule,sphincter and seminal vesicle penetration and also lymph node spread. In addition, if the index lesion is substantial and or associated with a Gleason 7 or above and located in the base or apex of the prostate, infiltration of the sphincter or base of the prostate is likely. These margins should be biopsied to check if the prostate cancer is outside the prostate and no longer localized and therefore unsuitable for a minimally invasive treatment.
Also, in multifocal prostate cancer, there is a greater risk of higher grade prostate cancer and therefore a higher Gleason score, stage and recurrence rate when compared to unifocal prostate cancer.
With these issues in mind, most of my patients with significant localized prostate cancer prefer total prostate ablation with a minimally invasive option such as HIFU rather than just focusing only on the index lesion (focal treatment) and disregarding treatment of the satellite lesions.
Finally, much of the prostate cancer data needs to be viewed with caution as few if any studies include independent validations of the prostate pathology and, also, prostate cancer is still something to be reckoned with as it is the second leading cause of male cancer deaths after lung cancer.