Can brachytherapy spread prostate cancer?

In an earlier commentary (see this link), we looked at the available evidence that invasive procedures, including surgery, biopsy, and brachytherapy, could spread prostate cancer. There have been very few cases reported where it is likely that brachytherapy has spread prostate cancer: 5 cases from seeds migrating to the lungs (see this link), and one case where a catheter probably spread the cancer to the bladder wall during high dose rate brachytherapy (see this link).

Tsumura et al. report the results of their study to determine whether circulating tumor cells (CTCs) were dislodged from the prostate into systemic circulation by brachytherapy. They took blood samples from 59 patients before and immediately following brachytherapy.

• 30 patients were treated with a combination of hormone therapy, external beam radiation, and high dose rate brachytherapy (HDRBT) for high risk or locally advanced prostate cancer.
• 29 low- and intermediate-risk patients were treated with low dose rate brachytherapy (LDRBT) as a monotherapy.

The blood samples were analyzed using CellSearch technology. They found that:

• None of the samples taken before brachytherapy had any CTCs
• CTCs were detected immediately after brachytherapy in 7 patients (11.8%), 13.3% among LDRBT patients, 10.5% among HDRBT patients.
• There was no statistically significant association with risk category, clinical stage, tumor volume, Gleason score, PSA, prostate volume, needle concentration, age, hormone therapy or type of brachytherapy.

While it is too soon to know whether those CTCs will cause a recurrence in the 7 brachytherapy patients, a similar study done by Eshwege et al. before and after prostatectomy suggests that they will not. In that study, there was increased risk of recurrence only if CTCs were found before the prostatectomy. The additional shedding of tumor cells during the procedure did not correlate with recurrence within 5 years.

Even high risk/advanced prostate cancer cells are not capable of survival outside of the prostate environment. To metastasize, they must first undergo a series of genetic alterations called epithelial-to-mesenchymal transition (EMT). Some researchers believe that small numbers of such metastatic-capable cancer cells may exist in small numbers within the prostate. If so, it seems to be a rarity.