MRI ‘good accuracy’ for detecting residual breast cancer

By Lynda Williams, Senior medwireNews Reporter

Magnetic resonance imaging (MRI) is superior to mammography for the detection of residual breast cancer after neoadjuvant chemotherapy, research confirms.

"Our meta-analysis has shown good overall accuracy for MRI, although accuracy estimates varied with the definition of [pathologic complete response] pCR, which highlights the importance of standardizing pCR definitions," say Michael Marinovich (University of Sydney, Australia) and co-authors.

The team collated data for 44 studies including 2050 patients with 2068 cancers, mostly stage II and III invasive ductal carcinoma.

The overall area under the summary receiver operating characteristic curve for MRI accuracy compared with pathologic results for surgical excisions was 0.88, with specificity and sensitivity values of 0.60 and 0.92, respectively.

Of note, accuracy was lower in studies where the definition of pCR excluded residual ductal carcinoma in situ than it was in studies which used a nonspecific definition of positive and negative pCR, or a "near-pCR" definition allowing microscopic clumps of cells, with relative diagnostic odds ratios (RDORs) of 2.41 and 2.60, respectively.

Subanalysis demonstrated that studies which identified pCR as being a complete absence of MRI enhancement had a lower specificity value than studies that defined a negative MRI result as being contrast enhancement less than or equal to healthy breast tissue (0.54 vs 0.83) . However, the two protocols had comparable sensitivity (0.87 vs 0.83).

Defining residual malignancy as being contrast enhancement less than or comparable to normal tissue may therefore increase the likelihood of false-positive diagnosis, the researchers suggest.

Mammography was significantly less accurate for differentiating between residual tumor and pCR than MRI (RDOR=0.27), but MRI provided only a weak improvement in accuracy over clinical examination (RDOR=0.54).

Furthermore, there was no significant difference in the accuracy of MRI and a relatively inexpensive ultrasound examination.

"However, relatively few studies reported direct comparisons between MRI and other tests, and the comparative accuracy of MRI and combined ultrasound and clinical examination warrants further investigation in well-designed clinical trials," Marinovich et al write in the Journal of the National Cancer Institute.

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