Radiology: Breast MRI markers may indicate response to therapy
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| Breast MRI Navigation software Image source: Sentinelle Medical |
Dynamic contrast medium-enhanced (DCE) and dynamic susceptibility contrast-enhanced (DSC) MR imaging can yield information on therapeutic response by enabling radiologists to assess changes in tumor vasculature, thus acting as an early response predictor, wrote Sonia P. Li, MBBS, of Mount Vernon Cancer Centre. Recent animal studies suggested that ISW MR imaging may offer a way to map breast tumor hypoxia.
Li and colleagues from the Academic Oncology Unit at Mount Vernon Cancer Centre in Middlesex, England, sought to investigate the histopathologic and dynamic MRI correlates of ISW MR imaging and assess the relationship between baseline transverse relaxation rate and T2 relativity changes and the response to neoadjuvant chemotherapy.
The researchers recruited 83 women with breast cancer between September 2001 and January 2008 to undergo DCE, DSC and ISW MR imaging before and after two cycles of neoadjuvant chemotherapy. Ultimately, 31 women were available for baseline assessment and 27 for response assessment.
Upon completion of therapy, a consultant pathologist compared the core biopsy with the surgical biopsy sample to grade patients on a five-point scale. Women with responses ranging from grade 1 (no evidence of residual invasive cancer) to grade 4 (macroscopic residual cancer with evidence of chemotherapy-induced changes) were characterized as responders. Grade 5 nonresponders had a macroscopic invasive cancer with no response to chemotherapy. Among the 31 women, 16 were characterized as responders and 11 as nonresponders.
Researchers calculated transverse relaxation rate (R2) values and T2 relaxivity change as well as determining relationships between R2 and histopathologic variables such as tumor grade and estrogen receptor status, as well as tumor size and dynamic MR parameters.
Li and colleagues found no correlation between mean R2 values and histopathologic variables or tumor size. However, they did note strong correlations between the transfer constant and the initial area under the gadolinium concentration-time curve at 60 seconds and between relative blood volume and relative blood flow.
Among the kinetic parameters, baseline initial area under the gadolinium concentration-time curve at 60 seconds and relative blood flow and relative blood volume predicted response, offered the researchers. Specifically, baseline initial area under the gadolinium concentration-time curve at 60 seconds was 15.92 in responders and 13.04 in nonresponders; relative blood volume was 324.5 in responders and 143.5 in nonresponders, and relative blood flow was 7.0 in responders and 2.9 in nonresponders.
Li and colleagues reported that changes in R2 after two chemotherapy cycles correlated with final pathologic response, with responders showing an increase in R2 (36.5 seconds vs. 31.7).
“The significant positive correlations observed between several DCE and DSC MR imaging kinetic parameters at baseline support our suggestion that treatment-naïve breast cancers are primarily flow dominated due to increased angiogenesis and microvessel permeability as a result of vascular endothelial growth factor upregulation,” wrote Li. What’s more, initial area under the gadolinium concentration-time curve, relative blood volume and relative blood flow may help identify patients who are more likely to have a pathologic response, suggested the researchers. That is, highly vascular cancers may have a better response to neoadjuvant chemotherapy, continued Li and colleagues.
The researchers acknowledged several limitations to the study including a small sample size and use of ISW as an indirect measure of tissue partial pressure of oxygen that may be confounded by multiple factors.
Li and colleagues indicated that radiologists should interpret changes in R2 with caution as the process is complex. However, “increases in R2 together with significant reductions in relative blood flow and relative blood volume as well as the disappearance of R2 correlations with relative blood volume and relative blood flow after two cycles of neoadjuvant chemotherapy, are consistent with R2 becoming a more robust surrogate marker of breast tumor hypoxia after treatment.”