MR + PET highlight elusive triple negative breast cancers

The heterogeneity of breast cancer can make it difficult to capture, especially in cases where telltale receptor expression or tumor characterization are not involved. However, MR and F-18 FDG PET may be able to suss out the more obscure phenotypes of the disease, according to a study published July 17 in Radiology.

Marjan S. Bolouri, MD, from the departments of radiology and biomedical imag­ing at the University of California, San Francisco, and colleagues conducted a retrospective study of invasive breast cancer patients who underwent dynamic contrast material–enhanced (DCE) MR imaging and FDG PET/CT be­fore treatment between January 2005 through December 2009 to determine their value in the assessment of advanced breast cancer, and particularly breast cancers that tested negative for both estrogen and progesterone receptor as well as overexpression of human epidermal growth factor receptor type 2, or triple negative (TN) breast cancer.

“Breast cancer is a heterogeneous disease that includes tumors with a broad range of therapeu­tic response, relapse risk, and overall prognosis,” wrote Bolouri et al. “Increased understanding of this diversity motivated the use of biologically based imaging to comple­ment the traditional anatomic-based modalities of mammographic imaging and ultrasonography (US).”

TN breast cancer is of interest because although it accounts for only 10-20 percent of breast cancer, it tends to be invasive and leads to a relatively high number of distant metastases and more cancer deaths. In addition to the lack of receptor involvement, these cancers also may lack the microcalcifications characteristic of other breast cancers that typically show up on mammograms. Contrast-enhanced MR with its high sensitivity and potential specificity and PET/CT may benefit patients with TN cancer especially due to the subtype’s inclination toward higher maximum standard uptake value (SUVmax) than other breast cancers. This could help clinicians identify TN breast cancer patients who stand a greater risk of early relapse. 

“This study provides additional support that imaging biomarkers, including dynamic contrast-enhanced MR imaging signal en­hancement ratio and SUVmax, relate to breast cancer aggres­siveness and therefore may be valuable for prognostic assessment,” the authors wrote.

Researchers targeted relationships between param­eters calculated with DCE MR and FDG PET/CT in 117 cases of primary invasive breast cancer. Results presented an escalation of high washout kinetics (1 percent) that was positively correlated with increases in SUVmax (1.57 percent). Similarly, a higher percentage of low plateau kinetics (also 1 percent) was associated with a decrease in SUVmax (1.19 percent). This was especially the case in TN tumors, which alone showed a 4.34 percent increase in SUV max per 1 percent increase in high washout and a 2.65 percent decrease in SUVmax per 1 percent increase in low plateau washout. These findings support previous research suggesting that certain types of breast tumors, including TN tumors, have unique characterization involving blood flow and tumor metabolism that deserves closer observation.

“There is increasing evidence that suggests a pathophysiologic com­monality that underlies angiogenesis and tumor glucose metabolism,” the researchers wrote. “Our findings underscore this complex relationship and suggest that it may differ based on the molecular subtype of a tumor. It is pos­sible that a high degree of concordance between blood flow and glucose metab­olism allows a tumor more biologic effi­ciency, thus conferring a more aggressive phenotype. We indeed found a stronger relationship between MR kinetics and SUVmax in the TN subtype, which sup­ported the hypothesis that blood flow and glucose metabolism are highly coupled in this more aggressive breast cancer sub­type.”

Further studies are needed to gain an understanding of the relationship of blood flow and tumor glucose metabolism and how this knowledge could be used to treat TN breast cancer and other complex cases of the disease.