Background and Purpose

High resolution magic angle spinning (HR-MAS) magnetic resonance (MR) spectroscopy provides a vast amount of biological information through the discrimination and quantification of various metabolites and may serve as a potential biomarker in breast cancer [1-3]. However, previous studies utilized either only core needle biopsy (CNB) or surgical specimens, and were based on a single small volume of tissue sample. Recently, there have been concerns that specimen type and intratumoral heterogeneity may affect biomarkers or metabolic profiling in breast cancer [4]. Therefore, we aimed to investigate whether intratumoral location and biospecimen type (in vivo collection of core biopsy samples or ex vivo collection of surgical tumor samples) affect the metabolic characterization of breast cancer assessed by HR-MAS MR spectroscopy.

Materials and Methods

This prospective study was approved by the institutional review board and informed consent was obtained. We analyzed 87 tumor tissue samples from 31 patients with invasive breast cancer, which were obtained from the center and periphery of the primary tumor after surgical removal and obtained preoperatively by CNB. Specimens were assessed with HR-MAS MR spectroscopy. Reliability and differences in HR-MAS MR spectroscopic values of metabolite concentrations between different specimen types were evaluated using the intraclass correlation coefficient (ICC) and paired t-test. ICC values that did not include 0 in their respective 95% confidence intervals were considered to show statistically significant agreement. ICC values in the following ranges were considered to indicate poor (0-0.2), fair (0.21-0.4), moderate (0.41-0.60), substantial (0.61-0.80) and almost perfect agreement (0.81-1.00). Multivariate analysis of spectral data was performed to evaluate whether different specimen types showed similar performance in distinguishing parent groups by hormone receptor status (ER, PR, HER2).

Results

There was a moderate or higher level of agreement between the concentrations of 94.3% (33 of 35) of the metabolites in the center and periphery of breast tumors. Between CNB and central surgical specimens, 82.9% (29 of 35) of the metabolites showed significant agreement, with 80.0% (28 of 35) showing moderate or a higher level of agreement. Among all three specimen types, all of the metabolites showed fair or a higher level of agreement, with 82.9% (29 of 35) showing moderate or a higher level of agreement. A heatmap illustrating metabolite concentrations for each tissue sample is shown as Figure 1. However, there was no significant agreement between the concentrations of phosphocholine (PC) and phosphoethanolamine (PE) in the center and periphery of breast tumors. Total choline (tCho, the sum of Cho, PC, and GPC) showed moderate agreement in all of the three comparisons (central surgical specimens vs. peripheral surgical specimens,and among all 3 specimen types). Using the paired t-test, most of the metabolites showed no significant difference between central and peripheral surgical specimens (97.1%, 34 of 35) and between CNB and central surgical specimens (94.3%, 33 of 35). Multivariate PLS-DA models showed similar diagnostic performances for predicting each hormone receptor status, regardless of specimen type (Table 1).

Discussion

Most of the HR-MAS MR spectroscopic values showed moderate to substantial agreement between the tumor center and periphery (94.3%) and between CNB and central surgical specimens (82.9%). Our study results suggest that overall, intratumoral location and biospecimen type have limited influence on HR-MAS MR spectroscopy data from breast cancer and thus, interpretation based on a single tissue sample is feasible for most metabolites. However, concentrations of PC and PE were most affected by specimen type, and did not agree between the tumor center and periphery or between CNB and central surgical specimens. Previous studies have shown that changes in PC, PE or tCho levels are detected after the administration of P13K inhibitors in breast cancer cells, and the potential role of MR spectroscopy for monitoring tumor response has been suggested [5-7]. Our study results suggest that caution is recommended in clinical decision-making based solely on PC and PE levels from a single tissue sample. Our study results also imply that metabolic profiling using multivariate analysis shows similar performance in the metabolic characterization of breast cancer, regardless of intratumoral location and biospecimen type, and can be readily applied in the analysis of breast cancer biopsy samples.

Conclusion

Overall intratumoral location and biospecimen type had limited influence on the metabolic characterization of breast cancer assessed by HR-MAS MR spectroscopy. However, some metabolites may be affected by specimen-related variables and caution is recommended in clinical decision-making based solely on metabolite concentrations from a single tissue sample.