Magnetic resonance imaging of the axial skeleton enables objective measurement of tumor response on prostate cancer bone metastases.

Background: There is currently no technique to image quantitatively bone metastases. Here, we assessed the value of MRI of the axial skeleton (AS-MRI) as a single step technique to quantify bone metastases and measure tumor response.

Methods: AS-MRI was performed in 38 patients before receiving chemotherapy for metastatic HRPCa, in addition to PSA, computed tomography of the thorax, abdomen, and pelvis [CT-TAP]; and Tc-99m bone scintigraphy. A second AS-MRI was performed in 20 patients who completed 6 months of chemotherapy. Evaluation of tumor response was performed using RECIST.

Results: Only 11 patients (29%) had RECIST measurable metastases in soft-tissues or lymph nodes on baseline CT-TAP. AS-MRI identified a diffuse infiltration of the bone marrow in 8 patients and focal measurable metastatic lesions in 25 patients (65%), therefore, doubling the proportion of patients with measurable lesions. Transposing RECIST on AS-MRI in 20 patients who completed 6 months of treatment, allows the accurate estimation of complete response (n = 2), partial response (n = 2), stable disease (n = 5), or tumor progression (n = 11), as it is done using CT-TAP in soft tissue solid metastases.

Conclusions: MRI of axial skeleton enables precise measurement and follow-up of bone metastases as it is for other soft-tissue metastasis.