Significance of Circulating Tumour Cells in Prostate Cancer Patients Receiving Adjuvant or Salvage Radiation Therapy
Radiation treatment to the prostate bed (where the prostate used to be) is the only form of treatment currently available for patients who have a rising PSA blood test after surgery. A rising PSA test suggests that there are prostate cancer cells left behind in the body, either in the site of the original surgery or elsewhere in the body. Alternatively some men have risk factors after their surgery that predisposes them to have a recurrence of their cancer soon after surgery. Unfortunately we don’t have any way to know where the prostate cancer cells are located in the body since bone scans and CT scans are not sensitive enough to detect small numbers of cancer cells. You are being asked to participate in this study to see if we can find prostate cancer cells in your blood. If we can find tumour cells then we can see if the numbers of cells declines after radiation which may predict for the success of radiation. This information can then be used to help patients and doctors decide if radiation is the right treatment for them.
Our primary objective is to correlate the number of CTCs with 2 yr biochemical disease free survival.
One secondary objective is to determine if CTCs can be used as an independent prognostic factor by looking at the relationship between the number of CTCs and other prognostic variables such as pre-treatment PSA, PSA doubling time, PSA free interval, Gleason score, presence of extra-capsular extension, positive margins and seminal vesicle invasion.
Metastasis from primary tumours is responsible for most cancer deaths. Adjuvant treatment with chemotherapy and/or radiation therapy is aimed at reducing the risk of metastasis. Many reports have suggested that early stage cancer has the potential to shed cancer cells into the circulation early in development; therefore the ability to detect these cells early and treat them appropriately has the potential to significantly improve patient outcomes . These circulating tumour cells (CTC’s) can be identified from the peripheral blood through the expression of epithelial and cancer specific markers. There are multiple approaches to detecting CTC’s but the most common is the CellSearch system. Recently, the CellSearch system was approved by the US Food and Drug Administration for routine clinical use in metastatic breast, prostate, and colon cancer. This system is the first automated, standardized and regulatory approved system for detecting and quantifying CTC’s in the peripheral blood. In multi-institutional studies it was able to detect CTC’s in approximately 70% of patients with metastatic breast cancer . Furthermore, Budd (2006) and Pachmann (2005) have noted that levels of circulating tumour cells in patients parallels the tumour burden and response to therapy thus these cells could be useful as prognostic and predictive factors in various cancers. One in 7 men over the age of 60 will be affected by prostate cancer in Canada . Radiation treatment to the prostate bed is a standard adjuvant and salvage treatment for prostate cancer patients [6-7]. The success of radiation can range anywhere from 20% to 77% . The primary explanation for this wide range is that radiation is a local treatment and poor responders to radiation have disease beyond the prostate bed at the time of radiation. Detection of CTCs could identify these patients such that other ‘non-local’ treatment could be offered and radiation could be avoided. As many as 38% of high risk patients will die of prostate cancer therefore, the identification of this poor prognostic group is essential .
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