Risk for secondary cancers after first-line radiation therapy for prostate cancer


There is a recognized risk for development of secondary primary cancers (SPCs) after first-line treatment with radiation therapy for localized prostate cancer. However, a new article suggests that newer forms of radiation therapy may have noticeably reduced that risk.

Huang et al. reviewed data from a cohort of 2,120 patients treated with various types of radiation therapy for their localized prostate cancer. The types of radiation included:

  • Conventional, two-dimensional external beam radiation therapy (2D-EBRT), used in 36 percent of patients
  • Three-dimensional, conformal EBRT (3D-EBRT) and intensity-modulated radiation therapy (IMRT), used in 29 percent of patients
  • Brachytherapy alone (BT), used in 16 percent of patients
  • 2D-EBRT with a brachytherapy boost (2D-EBRT + BT), used in 19 percent of the patients

The researchers also matched data on SPCs from these 2,120 patients on a 1:1 basis with a series of surgical patients based on the patients’ ages and length of follow-up.

The results of this analysis are as follows:

  • Overall risk for SPCs — regardless of follow-up time — was not significantly higher in the radiation therapy patients than in the surgery patients (hazard ratio [HR] = 1.14).
  • At > 5 years of follow-up there was a significant risk for SPCs in the radiation therapy patients compared to the surgery patients (HR = 1.86).
  • At >10 years of follow-up, the risk for SPCs in the radiation therapy patients compared to the surgery patients was further increased (HR = 4.94).
  • When broken down by type of radiation, the overall relative risk for SPCs compared to surgery was
    • HR =1.76 for 2D-EBRT
    • HR =0.81 for 3D-EBRT/IMRT
    • HR = 0.53 for BT
    • HR = 0.83 for 2D-EBRT + BT
  •  The types of SPC occurring most commonly among the patients receiving primary radiation therapy were bladder cancers, lymphoproliferative cancers (e.g., non-Hodgkin’s disease), and sarcomas.

It appears from these data that the only type of primary radiation therapy that increased overall risk for SPCs in this patient population (compared to surgery) was 2D-EBRT — classical radiation therapy that is rarely used today as first-line therapy for localized disease. However, the abstract to the paper does not provide a breakdown of either year of initial therapy or length of follow-up by type of radiation, so if (for example) 10-year follow-up data was only available for the 2D-EBRT patients, the results could be skewed in a manner that would perhaps be misleading. However, the authors clearly conclude that, “Radiation-related SPC risk varies depending on the [radiation therapy] technique and may be reduced by using BT, [BT + 2D-EBRT], or 3DCRT/IMRT.

6 Responses

  1. 2D being the only form of radiation that has 10 year data is a significant concern I have for this study. My position is and has always been that the term of prostate cancer studies is always way too short. 10 years is still inconclusive and therefore we have little data on the other forms of radiation in regards to SPCs. That stated I concede that we are delivering radiation better today than ever. But we do not have clear data on SPCs, other complications, and also — most importantly — prostate cancer-specific survival.

  2. I understand the concern regarding the follow up period, but I wonder if IMRT and BT were available 10 years ago. Does anyone know when were IMRT and BT introduced as standard therapy methods?

    Reuven

  3. IMRT and BT have both certainly been available at major academic centers for > 10 years. The unknown element is only how long they have been available at the specific center which accumulated this cohort of patients.

  4. As regular readers will know, it doesn’t take much to confuse me, and I am confused here.

    On the one hand this says, “Overall risk for SPCs — regardless of follow-up time — was not significantly higher in the radiation therapy patients than in the surgery patients.

    NOT signficantly higher = good , but … “at 5 years of follow-up there was a significant risk for SPCs in the radiation therapy patients compared to the surgery patients and at 10 years of follow-up, the risk for SPCs in the radiation therapy patients compared to the surgery patients was further increased.

    IS signficant, increasing risk = bad?

    And why no proton beam therapy in the study, given the claims for safety in that mode of therapy?

    As I say, just confused — put it down to Zoladex, as others have.

  5. Why no PBRT? That one is easy. These researchers didn’t have a PBRT machine to treat patients with. The only one available 10 years ago (or even 5 years ago I think) was the one at Loma Linda.

    Why does the risk go up over time? Could be any one of many reasons. It could take 5 or 10 years, for example, for a radiation-induced mutation to grow into a clincially signifciant tumor. We do know that if you follow any series of heavily radiated patients, their risk for secondary tumors increases over time — but part of that is just ‘cos they are getting older anyway. As we get older our risk for almost all cancers increases.

  6. I wish I knew the answer!! Seventeen years since RP, I have a PSA of 2.41 and remain symptom free. I have not had any radiation or chemo to date. Rather I went on an ultra-low-fat, mainly vegetarian diet, exercise, and, for 10 or so years, have taken orlistat (Xenical) which removes most of remaining dietary animal fat and hydrogenated fats.

    While there is no doubt that it has worked for me, who knows if it will work for their own prostate cancer? I wish I knew for sure.

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