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. © 2005 Wiley‐Liss, Inc.