Role of 18F-FDG PET/CT in evaluation of recently diagnosed breast cancer patients – Egyptian Journal of Radiology and Nuclear Medicine

Breast cancer is the most frequent cancer and the main cause of cancer-related mortality worldwide in women, affecting both elderly and young patients. Once breast cancer has been detected, the tumor stage must be precisely evaluated before therapy and prognosis can be determined [9].

Clinical examination of cancer patients is essential for initiating and monitoring treatment. The findings of CT can be improved by using the extra functional information offered by FDG PET, especially in the follow-up of cancer patients following surgery, radiation treatment, or chemotherapy [10, 11].

FDG PET is superior to conventional CT in the aspects of initial cancer assessment and progression. Mild metabolic activity in FDG PET may lead to misleading results, which may be confused with natural physiological activity. Added CT scans may help the detection of pathological sites for FDG accumulation [12].

Axillary lymph node involvement and/or the existence of distant metastases cannot be detected accurately by conventional imaging, which changes the therapeutic treatment of these patients dramatically. Whole-body ¹⁸F-FDG PET/CT has shown to be a useful imaging tool for malignant tumor staging. Furthermore, PET/CT can somewhat overcome the poor specificity of PET caused by the elevated glucose metabolic activities of benign tumors and inflammatory tissues [13].

The combination of PET and CT images enables integrated morphologic and functional imaging with a single scanner. The added functional information by FDG PET improves the evaluation of ambiguous CT finding, particularly in the follow-up of cancer patients who have had surgery, radiation therapy, or chemotherapy [14,15,16].

In general, FDG PET scans evaluated the pathologically elevated radiotracer uptake both quantitatively and quantitatively [17]. The SUV is elevated in malignant tumors than in benign lesions [18].

The mismatch between CT and PET images caused by patient breathing has serious consequences in evaluating areas near the heart, diaphragm, and lung bases, which may interfere with the interpretation of lung nodules [19]. To reduce misregistration, CT and PET scans were performed during shallow breathing in our studies, as Townsendetal et al. did [20].

Problems were frequently seen in diabetes patients because hyperglycemia inhibits ¹⁸F-FDG absorption into the cells; therefore, blood glucose levels above 200 mg/dl result in considerable alterations in ¹⁸F-FDG distribution. All of the participants in this research are within the suitable range of blood glucose level for injection.

The use of CECT in PET/CT assisted in improved characterization and anatomic localization of lesions, although contrast-enhanced pixel scan has the potential to cause focal artifacts in PET images, which is undesirable for tumor imaging [21].

In our study, we did PET with low-dose CT for attenuation correction, followed by contrast-enhanced CT for fused images. According to Bernsdorf et al., CECT is not used for attenuation correction; therefore, we did not have to deal with quantitative overestimation of ¹⁸F-FDG activity or artifactual hot spots in the attenuation-corrected images [22].

The main goal of this study is to evaluate the diagnostic performance of ¹⁸F-FDG PET/CT as a pre-therapeutic and preoperative assessment tool. Many previous studies revealed its superiority compared to other conventional modalities in alteration of initial patient staging. It was accurate in staging, which was crucial for the management of breast cancer patients.

In this study, combined PET/CT was demonstrated to be better than CT alone in detecting primary malignant breast tumors in the examined 50 patients, as PET/CT detected all 54 lesions compared to 52 lesions recognized by CT alone. These two lesions were tiny and could not be distinguished from surrounding glandular breast tissue on CT, although exhibiting significant metabolic activity in corresponding fused PET/CT images.

This agreed with prior research by Bernsdorf et al., who reported 97% sensitivity of PET/CT in detecting the breast tumors [22]. Furthermore, better sensitivity of FDG PET over CT alone was found by Mahner et al., that revealed 93% sensitivity of FDG–PET for detection of breast lesions compared to 88% of CT in patients with recently diagnosed breast cancer [23]. Fuster et al., in a trial on 60 patients, found that combined PET/CT could identify primary tumors in all the patients [4]. Tatsumi et al. [6] demonstrated that PET/CT is superior to PET or CT alone for the diagnosis of breast cancer.

In addition, although there was no statistically significant difference in this trial, combined PET/CT revealed metastatic axillary lymph nodes in 38 patients compared to 35 patients with CT alone.

This study matched with Tatsumi et al., who found that combined PET/CT was preferable to CT alone in detecting metastatic axillary lymph nodes as small lymph nodes usually interpreted negative by CT. As a result, PET/CT may be useful in prediction of patient outcomes, as patients with nodal metastasis have poorer prognosis than patients without nodal affection [6].

Many previous studies have shown that combined PET/CT had high specificity (90–100%), positive predictive value and sensitivity (63–70%) for detecting axillary nodal metastasis and can accurately differentiate reactive from metastatic lymph nodes when multiple enlarged axillary lymph nodes are seen in CT [4, 22, 24, 25].

Our study also revealed that combined PET/CT was better than CT alone in detecting extra-axillary nodal involvement. In 14 patients (28%), combined PET/CT revealed distant nodal metastasis, while CT alone detected them in just 11 patients (22%). Combined PET/CT found contralateral axillary nodal deposits in 5 patients, but only in 3 patients by CT alone. This discrepancy can be explained by the substantial metabolic activity by the combined PET/CT in tiny sub-centimetric lymph nodes that were negative on CT.

We also agreed with a study by Choi et al. who revealed that combined PET/CT was more efficient than contrast-enhanced CT in localizing extra-axillary nodal involvement [26]. According to Aukema et al., FDG PET/CT is a beneficial imaging technique to identify extra-axillary lymph node metastases, which may have an influence on adjuvant radiation treatment [27].

Breast cancer distant metastasis is usually seen in the lungs, liver, and bones. The ability to identify metastases at several organs and locations in a single examination is one advantage of whole-body PET/CT imaging compared to other imaging techniques [28].

Out of 50 patients included in the study, fused PET/CT revealed pulmonary and visceral metastases (including the liver, spleen, and suprarenal glands) in 8 patients, while recognized in 7 patients by CT alone. Furthermore, fused PET/CT identified osseous deposits in 16 patients, whereas CT alone showed osseous deposits in 14 patients. This study showed overall better performance of combined PET/CT than CT alone in detecting distant metastases.

Our study matched with Bernsdorf et al. who showed that PET/CT is a useful method for detecting extra-axillary nodal involvement, distant metastases, and other occult primary tumors. They revealed that preoperative FDG PET/CT scanning had a significant influence on staging and subsequent management [22].

This is consistent with the findings of other studies by Choi et al., Groheux et al., and Morris et al., who found that ¹⁸F-FDG PET/CT has higher overall sensitivity and specificity in detecting distant metastases than conventional imaging and is also preferable in evaluating breast cancer lesions [26, 29, 30].

The main limitation of this study was the relatively small sample size; therefore, prospective studies in the future with a larger number of patients will more clearly define the role of PET/CT-based evaluation with more accurate results.