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Imaging, Diagnosis, Prognosis |
Authors' Affiliations: 1 Division of Nuclear Medicine, Hôtel Dieu and 2 Division of Biostatistics, Hôpital St. Jacques, CHU Nantes, France; and Divisions of 3 Medical Oncology and 4 Nuclear Medicine, CHU Liège, University of Liège, Liège, Belgium
Requests for reprints: Roland Hustinx, Division of Nuclear Medicine, CHU Sart Tilman, B35 4000 Liège 1, Belgium. Phone: 3243667199; E-mail: rhustinx{at}chu.ulg.ac.be.
| Abstract |
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Experimental Design: Twenty patients with hormonorefractory or hormonoreceptor-negative multimetastatic breast cancer were prospectively included. PET studies were done at baseline, at day 21 after the first cycle and at day 21 after the third cycle of chemotherapy. Metabolic response was defined based on visual and various modes of standardized uptake value (SUV) analysis of sequential PET studies.
Results: After one cycle, PET indicated a partial response in 12 patients, stable disease in 7 patients, and progressive disease in 1 patient, according to the visual analysis. After three cycles, PET showed a complete response in 5 patients, partial response in 11 patients, stable disease in 3 patients, and progressive disease in 1 patient. Seventy-five percent of the patients showing a metabolic response on visual analysis effectively responded to the treatment. The average SUV decreased on both the second and the third PET study, but only changes measured after three cycles of chemotherapy predicted the clinical response to chemotherapy and the overall survival. All methods for calculating the SUV (normalized for body weight, body surface area, or lean body mass) provided similar results.
Conclusion: Semiquantitative analysis of [18F]fluorodeoxyglucose-PET studies done after three cycles of chemotherapy is useful for monitoring the response to chemotherapy in metastatic breast cancer.
The aim of this study was to evaluate whether PET done after one and three cycles of chemotherapy could predict the short-term response to chemotherapy, as measured at 6 months, and the long-term objective response to chemotherapy [event-free survival (EFS) and overall survival (OS)]. A secondary aim was to verify whether visual analysis and various methods for calculating the standardized uptake value (SUV) done equally as predictive variables.
| Materials and Methods |
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PET studies. All studies were done using the C-PET scanner (UGM-Philips, Milpitas, CA). The system has been fully described elsewhere (9). All patients fasted for at least 4 hours before tracer injection. Blood glucose level was measured in each case and did not exceed 7.77 mmol/L (140 mg/dL). Patients were injected i.v. with 3.9 ± 0.5 MBq/kg FDG (mean ± SD, 0.105 ± 0.014 mCi/kg) through an indwelling catheter. Acquisition was started 69 ± 13 minutes postinjection (mean ± SD; range, 53-94) for the first scan, 71 ± 21 minutes postinjection (range, 47-118) for the second scan, and 71 ± 12 minutes postinjection (range, 49-91) for the third scan. There were no statistically significant differences among these uptake times. The PET acquisition consisted of five or six bed positions. Five-minute emission scans, 1-minute transmission scans using a 137Cs point source, and 8-second emission contamination scans were interleaved. Images were reconstructed using the ordered subset-expectation maximization algorithm and corrected for decay, scatter, random coincidences, and attenuation.
Data analysis. PET studies were done at baseline (PET1), at day 21 after the first cycle (PET2) and at day 21 after the third cycle (PET3) of chemotherapy. The tumor marker CA15.3 was increased at baseline in 12 of 20 patients. We only followed the tumor marker level after one and three cycles of chemotherapy in these patients. The metabolic response based on visual analysis of sequential PET studies was assessed according to European Organization for Research and Treatment of Cancer 1999 recommendations (10): (a) complete response for complete resolution of [18F]FDG uptake within the tumor volume (indistinguishable from surrounding normal tissue); (b) partial response for a significant decrease in tumor uptake and/or a decrease in the total number of hypermetabolic lesions; (c) stable disease for no visible increase of tumor uptake and the absence of new hypermetabolic lesions; and (d) progressive disease for a visible increase in tumor uptake or new hypermetabolic lesion(s). Any focus visualized in the three planes and which did not correspond to physiologic activity was considered as abnormal. Furthermore, semiquantitative analysis of [18F]FDG uptake (SUV) was done using the median value of SUV changes between PET1 and PET2 and between PET1 and PET3: tumors showing changes greater than the median value were considered as responders and those showing changes equal or lower than the median value were considered as nonresponders.
Regions of interest were placed visually in the transversal slice over focal lesions, in which [18F]FDG accumulation was the highest. The regions of interest followed an isocontour at 60% of the maximum pixel value. Average and maximum SUVs normalized for body weight (SUVBW), for body surface area (SUVBSA), and for lean body mass (SUVLBM) were calculated using the following equations (10, 11):
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Statistical analysis. Paired Wilcoxon's tests were used to compare injected doses and SUV values between the three PET examinations. Mann-Whitney U tests were used to compare changes in SUVs between PET1 and PET2 and between PET1 and PET3. Relationship between metabolic response (patients stratified according to the median value of SUV variations) and clinical response was analyzed by Fisher's exact tests. EFS and OS were determined by standard Kaplan-Meier survival analysis, and comparison between groups was done by the log-rank test. EFS was defined as the time interval from the date of enrollment in the study until progression, relapse, death, or date of last follow-up. OS was calculated from the date of enrollment until death from any cause. Relationships between SUV values on PET1, PET2, or PET3 and survival were also evaluated using a linear regression model. If these relationships were not linear, Spearman's correlation coefficients were calculated. Relationship between changes of tumor markers CA15.3 and changes of SUV were evaluated using a linear regression analysis between CA15.3 slopes and SUV slopes for each patient. Regression models assumed residual normality and homoscedasticity, both of which being graphically verified. In all cases, the level of significance was set at 0.05. All analyses were done using Graphpad prism version 4.0b 2004 (Graphpad Software, San Diego, CA).
| Results |
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The clinical response measured at 6 months using conventional methods predicted the OS but not the EFS (Fig. 3 ). Similarly, the metabolic response measured as changes in SUV after the third cycle of chemotherapy predicted the OS but not the EFS (Fig. 4 ). However, early changes in SUVs (after the first cycle of chemotherapy) were not predictive of the long-term outcome (Fig. 5 ).
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| Discussion |
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[18F]FDG-PET was also proposed for monitoring the response of breast cancer to chemotherapy and thus guide therapeutic regimen. The assessment of the response to therapy by PET is based on the reduction or the complete abolition of the tumor [18F]FDG uptake, depending on the reduction of the tumor glucose metabolism or cellular death, respectively. Such approach was applied for assessing the response to chemotherapy given before surgery (neoadjuvant chemotherapy). [18F]FDG-PET may provide an earlier and noninvasive evaluation, which offers the possibility to modify early on therapeutic regimen to improve the likelihood of obtaining a complete response. Preliminary studies with small cohorts of patients showed a correlation between the early reduction of the tumor [18F]FDG uptake and the clinical response at the end of neoadjuvant chemotherapy (15, 16). No such decline was observed in patients who did not achieve a partial or a complete response. In contrast, conventional imaging studies failed to determine the treatment response as early on as PET did. Further studies with larger series showed that the early reduction of tumor [18F]FDG uptake was correlated with the macroscopic response at the end of neoadjuvant chemotherapy (1719). However, the SUV cutoff values for discriminating responders from nonresponders varied among the studies. For instance, in the study of Schelling et al. (18), the nonresponding patients presented on average a reduction of [18F]FDG tumoral uptake of 15%, whereas Smith et al. (17) reported an average increase of 43% for the nonresponders. Likewise, by using a receiver operator characteristic analysis in the study of Schelling et al., a decrease in SUV after the first cycle of chemotherapy to <55% of baseline discriminated between responders and nonresponders (sensitivity of 100% and specificity of 85%), whereas, in the study of Smith et al., a 20% reduction in [18F]FDG uptake after the first cycle of chemotherapy predicted the response to therapy with a sensitivity of 90% and a specificity of 74%. Differences in the cutoff values for the SUVs may be explained not only by the high variability of breast tumor biology but also by the methodology used to assess the metabolic activity, including the type of region of interest and method for calculating the SUV.
In contrast to the previous studies in the neoadjuvant setting, we assessed early on the response to chemotherapy by PET in multimetastatic breast cancer. There are very few data in the literature in this field. In a small study of 12 metastatic breast cancer patients, Gennari et al. (20) observed a significant decrease in tumor glucose metabolism after the first cycle of chemotherapy in patients who responded to treatment. In contrast, no significant decrease was reported in case of treatment failure. Schwartz et al. (7) evaluated 11 patients with 26 metastatic lesions after one and two cycles of chemotherapy. The decrease in FDG uptake was higher in responding lesions than in the nonresponding locations. In addition, visual analysis of the PET images was able to predict the overall response to treatment. There was also a trend toward longer survival in metabolic responders, although it did not reach statistical significance.
Our results somewhat contradict those previously published in the literature. Indeed, our primary hypothesis is only partly verified: In our series, PET was able to predict the short-term response to chemotherapy and the OS, but only when it was done after three cycles of chemotherapy. In fact, PET done after three cycles of chemotherapy provided results that were very similar to those obtained with conventional methods after completing the treatment. When the metabolic response was evaluated after one cycle of chemotherapy, neither the visual analysis nor the changes in SUVs were able to reliably predict the short-term outcome (clinical response at 6 months) or the long-term outcome (EFS and OS). It seems clearly that PET is more predictive at midcourse than early on during treatment, but statistically, our population is not large enough to rule out a potential role for the early PET. An obvious question arises considering these results: if PET predicts the outcome at midcourse of treatment; would it provide any additional and clinically relevant information compared with conventional methods done at the same time? Our study was not designed to answer this question, as all lesions were not systematically evaluated using conventional technique after three cycles. It is well known however that these techniques are unable to correctly evaluate response after only one cycle (21). The difficulty to assess both the early and the late responses in bone metastases, which are highly prevalent in this population, is also well known. Tumor markers are not very useful either, as up to 25% of patients show an initial increase while responding positively to treatment. Our study confirmed this observation, as the median tumor marker level was higher after one cycle that at baseline, and it became lower after three cycles. Changes in CA15.3 level and in SUV measured during chemotherapy were not similar in trend, as none of our patients presented an initial increase in [18F]FDG uptake before responding to treatment.
Although PET was not predictive after one cycle and its added clinical value was not fully established after three cycles, we believe that our results are clinically relevant. It is important to point out that such prediction of outcome was obtained using a very simple method (i.e., the evolution of SUV in the most active lesion identified throughout the entire body). The capability of PET, as a single procedure, to reach such conclusion provides several advantages over alternative methods, whose diagnostic performances vary highly according to the site of the lesions. PET, on the other hand, is both sensitive and specific for detecting malignant involvement of the liver, lung, skeleton, and lymph nodes (1). Further studies are needed to compare conventional techniques, either targeted for evaluating selected lesions or as a battery of tests (systematic combination of chest CT, abdominal CT, bone scintigraphy, or MRI) with a single one, PET or, given a technological developments that is increasingly available, PET/CT.
About the methodologic aspects, we found that semiquantitative analysis provided better results than the simpler visual analysis and that there were no significant differences according to the various methods for calculating the SUVs. In our series, the variation in body weight during chemotherapy was not sufficient to introduce a bias in the measurements of the metabolic activity when the SUV is normalized for the body weight. In addition, we did not normalize the SUVs for blood glucose levels, as previous studies in healthy subjects showed greater within-patient variability in SUV measurements when such correction was applied (22). The question of which approach of region of interest methods gives the best results for tumor response assessment has yet to be answered. In our study, we used one of the commonly used methods (i.e., a 60% threshold-based region of interest method), which is simple and user independent and which gives results relatively independent of lesion size and geometry (23).
The capability of PET to separate responders from nonresponders after three cycles of chemotherapy may be of value for the development of new drugs. Indeed, only those patients with an early response are candidates to continue the treatment. An early change to standard treatment is indicated for the other patients. Furthermore, many new drugs are more cytostatic than cytotoxic and conventional imaging techniques are largely inappropriate for evaluating the response in these circumstances. Assessment of metabolic changes may well be better suited for monitoring the response to these treatments. Finally, early response evaluation may be particularly important when a second-line treatment with curative intent is available. This is the case for example in non-Hodgkin's lymphomas (24).
| Conclusion |
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| Footnotes |
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Received 2/17/06; revised 7/ 7/06; accepted 8/16/06.
| References |
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