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MRI can track bone mets treatment response in prostate cancer

Prostate Cancer Bone Mets: Tracking Response to Treatment Using MRI

MRI offers new hope for evaluating how well prostate cancer bone metastasis (PCa bone mets) are responding to chemotherapy. An exciting new paper (April, 2017) by a British team at the Institute of Cancer Research (Sutton, England) reports their original pilot study confirming MRI tracking success.i

The authors explain that when advanced prostate cancer (PCa) no longer responds to androgen deprivation therapy and begins to spread (metastatic castration-resistant prostate cancer or mCRPC), about 84% of patients will have bone mets. Standard CT imaging and bone scintigraphy are often not accurate in assessing the extent and volume of the bone mets, nor can they accurately tell how well the mets are responding to chemotherapy treatment. The PSA blood test is also not a reliable indication of treatment progress. This is disheartening for doctor and patient alike.

A very specific use of magnetic resonance imaging (MRI) called diffusion-weighted imaging (DWI) can detect PCa, including bone mets, by revealing the motion of water molecules within tissue. In normal cells, water molecules move more freely than they do in cancer cells. DWI can actually register the amount of restriction. Different tumors have characteristic restriction values specific to that tumor, and so it is with bone mets. The DWI signal intensity on the scan is the telltale measure of the total diffusion volume (tDV) of the lesions. In four small studies from 2007-14, researchers demonstrated that scanning a patient using MRI with DWI could identify the location and tDV of PCa bone mets. Therefore, the authors of the 2017 paper hypothesized that whole body MRI/DWI could be used to monitor how well chemotherapy was working to shrink bone mets.

In the 2017 study, the chemotherapeutic agent was olaparib, a drug that targets cancers with the genetic mutations BRCA1 and BRCA2 (first identified in breast cancer). It is now known that these mutations can exist in PCa patients with a family history of BCa. If mCRPC bone mets patients have either mutation, there is a chance that their bone tumors will respond to olaparib – but not a guarantee.
Twenty-one patients with PCa bone mets were enrolled in the 2017 study. All underwent a baseline whole body MRI/DWI scan on a 1.5T magnet, and their bone mets were identified both by visual volume and by water molecule motion as a qualitative evaluation of the lesions. After 12 weeks of being on olaparib, they were again scanned. It was found that 6 of the patients had responded positively to the anticancer effect of the drug, as confirmed by reductions in tDV shown on DWI. These reductions were correlated both with the patients’ lowered PSA and the reduced number of circulating tumor cells in the bloodstream. In short, DWI functioned as a successful response biomarker.

Although the 2017 study had a small sample size, it is still the largest series to date using whole body MRI/DWI to monitor bone mets treatment response in mCRPC patients. The authors point out that “…these data indicate that whole-body DWI may have a role in bone metastases response assessment in mCRPC, without the need for ionizing radiation or intravenous contrast material…” Many patients are concerned about exposure to radiation (CT scans) or the radioactive isotopes used in bone scan contrast agents, while MRI is radiation-free. In addition, whole body MRI/DWI has the potential to detect mets in soft tissue and lymph nodes as well as bones, giving more detailed information about a patient’s burden of disease.

The ability to evaluate treatment response has distinct benefits, including

  • Developing a prognosis for term of survival and quality of life
  • Identifying a follow-up monitoring protocol
  • Planning further treatment strategies
  • Managing patient expectations
  • Boosting patient sense of control after feeling loss of control

Both the Sperling Prostate Center and the Sperling Medical Group provide 3T multiparametric MRI with advanced DWI capability. In addition, the Sperling Medical Group offers MRI-guided Focused Ultrasound (MRgFUS) for targeted ablation of bone mets and relief from pain. For more information, contact the Sperling Medical Group.

iPerez-Lopez R, Mateo J, Mossop H, Blackledge MD et al. Diffusion-weighted imaging as a treatment response biomarker for evaluating bone metastases in prostate cancer: a pilot study. Radiology. 2017;283(1):168-77.

Bone mets