Background: This study was designed to investigate the fluorine-18 fluorodeoxyglucose (FDG)-positron emission tomography (PET) imaging characteristics of triple-negative (estrogen receptor-negative [ER-]/progesterone receptor-negative [PR-]/HER2-negative [HER2-]) breast carcinoma and compare the results with characteristics of ER+/PR+/HER2- breast carcinomas, which usually carry a favorable prognosis.
Methods: Patients with newly diagnosed breast carcinoma who had undergone dual-time-point FDG-PET before any therapeutic intervention and were identified as either ER-/PR-/HER2- or ER+/PR+/HER2- (the control group) on histopathology of the surgical specimen, were considered candidates for inclusion in this analysis. These patients underwent FDG-PET as a component of a prospective study that evaluated the role of multimodality imaging for characterizing primary breast lesions and locoregional staging. Breast cancer lesions were imaged twice at approximately 63 minutes and 101 minutes after the administration of FDG. Maximum standardized uptake values (SUVmax) were measured at both time points (SUVmax1 and SUVmax2) to analyze the data generated. After FDG-PET imaging, the patients underwent either breast-conserving surgery or mastectomy, and histopathology reports were used to provide the definitive diagnosis against which the PET study results were compared.
Results: In total, 88 patients with breast cancer (29 patients with 'triple-negative' breast cancer and 59 patients with ER+/PR+/HER2- breast malignancies) were selected among 206 individuals who were enrolled in the study protocol. The 'triple-negative' group comprised 14.08% of the total study population. The age of the patients with this subtype of tumor ranged from 33 years to 75 years (mean age+/-standard deviation, 51.6 +/- 10.1 years), and tumors in this subgroup ranged in size from 0.9 cm to 6 cm (mean size, 1.99 cm). Among the histopathologic subtypes, 25 tumors were infiltrating ductal carcinoma (86%), and 1 tumor each (3.5% each subtype) was lobular, mixed ductal-lobular, medullary, and tubular. For the calculation of FDG-PET parameters in this group, only patients who had undergone FDG-PET studies before any intervention were considered, and 18 patients in the triple-negative group met this criterion. According to same criterion, a control group of 59 patients with ER+/PR+/HER2- cancer who had focal FDG uptake were selected for comparison with the triple-negative population. The breast cancer lesions were observed as areas with focally enhanced uptake of FDG in all patients (sensitivity, 100%) in the triple-negative group. The mean (+/-standard deviation) SUVmax1 of the primary lesion for the triple-negative group was 7.27 +/- 5.6, the mean SUVmax2 was 8.29 +/- 6.4, and the percentage change in SUVmax (%DeltaSUVmax) was 14.3 +/- 15.8%. In the control group of 59 patients with ER+/PR+/HER2- breast carcinoma, the mean values for SUVmax1, SUVmax2, and %DeltaSUVmax were 2.68 +/- 1.9, 2.84 +/- 2.2, and 3.7 +/- 13.0%, respectively. The mean values for SUVmax1, SUVmax2, and %Dgr;SUVmax in the triple-negative group were significantly higher compared with the values in the nontriple-negative control group (P = .0032, P = .002, and P = .017, respectively). When the 2 subgroups were compared according to tumor size, grade, and stage, the SUVmax1 was significantly higher in the triple-negative group for both size categories (5.4 vs 1.9, P = .006; and 9.2 vs 3.5, P = .04) and for grade 3 tumors (9.1 vs 3.9, P = .022). The %DeltaSUVmax values for patients in the triple-negative group who had tumors that measured < or =2 cm and > 2 cm were 14.8 and 13.8, respectively; and the corresponding values for patients in the control group were 0.6 and 6.7, respectively. Although the mean %DeltaSUVmax clearly was higher in the triple-negative group for both tumor size categories, comparison between the 2 groups demonstrated a statistically significant difference in tumors that measured < or =2 cm (P = .016). The authors also observed that, in the triple-negative group, tumor grades were correlated significantly with the magnitude of SUVmax1 and SUVmax2 (P = .012 and P = .01, respectively). Stage for stage, tumors from the triple-negative group appeared to have a higher mean SUVmax1 compared with tumors from nontriple-negative control group. However, the trend reached statistical significance in patients with stage II disease.
Conclusions: Triple-negative breast tumors were associated with enhanced FDG uptake commensurate with their aggressive biology and were detected with very high sensitivity by using FDG-PET imaging.