The most widely used biomarker in the prediction and management of OC recurrence is the CA125 [9]. However, lack of specificity is the major problem facing the use of serum CA125 in diagnosing OC recurrence. CA125 may be elevated in other malignant or benign diseases such as pancreatic, breast, and endometrial cancers [10].

In literature, the reported CA125 value denoting OC recurrence has 62–94% sensitivity and 91–100% specificity [11, 12]. In this study, elevated CA 125 level (> 35 U/ml) in detecting OC recurrence during patient follow up, CA125 level had an accuracy of 50% with sensitivity and specificity of 47% and 80%, respectively. CA125 level had a PPV of 95% and a NPV of 14%, indicating a moderate diagnostic performance of CA125 level in detecting recurrent ovarian cancer.

In accordance with our results, Hopkins et al. did not find any prognostic benefit for the use of CA125 level alone for detecting of recurrent OC. They recommended the use of CA125 level only for OC surveillance [13].

Also, Gronlund et al. documented that CA125 concentration is not a sufficient independent prognostic factor for recurrence in different cut-off [14].

In contrast, in the Gu et al. meta-analysis, the CA125 recorded the highest specificity (93%) in diagnosing OC recurrence [15].

Yang et al. found that the sensitivity and specificity of serum CA125 for diagnosing epithelial ovarian carcinoma recurrence were 67.39% and 86.79%, respectively [16].

The undetected or inconclusive in cross sectional imaging, 18F-FDG PET/CT plays a crucial role in the confirmation or exclusion of suspected ovarian cancer recurrence. So, when suspicion of radically treatable disease recurrence is confirmed, this study provides additional information in the detection of non-suspected disease, also it altering the initially proposed therapeutic management protocol [17].

In this study regarding 18F-FDG-PET/CT behaviour in the detection of OC recurrence during patient follow-up, 18F-FDG-PET/CT had an accuracy of 98% with sensitivity and specificity of 98% and 100%, respectively. 18F-FDG-PET/CT had PPV of 100% and a NPV of 83%, indicating an excellent diagnostic performance of 18F-FDG-PET/CT level in the detection of ovarian cancer recurrence.

Batra et al. reported that the sensitivity, specificity, PPV, NPV, and accuracy of PET-CT to detect OC recurrence were 90%, 66.7%, 83.7%, 77.7%, and 81.9%, respectively. These measures are lesion-based compared to histopathology, not patient-based, which may explain the low accuracy of PET/CT in this study [18].

Additionally, Tawakol et al. concluded that 18F-FDG PET/CT is superior to CECT concerning the diagnosis of OC recurrence. 18F-FDG PET/CT and CECT had a sensitivity of 92 versus 59%, a specificity of 96 versus 84%, PPV of 90 versus 59%, NPV of 97 versus 84%, and accuracy of 95 versus 76%, respectively [19].

Furthermore, Limei et al. noted that the specificity, sensitivity, positive and negative ratios, and the area under the curve of PET/CT scan that detect OC recurrence was 91.0%, 89.7%, 6.140%, 0.123%, and 0.9497%, respectively [20].

Moreover, Hebel et al. retrospectively studied 48 cases with suspicious recurrent OC who were referred for 18F-FDG-PET/CT. The recorded 18F-FDG-PET/CT sensitivity and PPV of 97% and specificity and NPV of 90% as in one case, 18F-FDG-PET/CT scan showed false-positive result and in another case showed false-negative result. Most patients changed the management modalities after 18F-FDG-PET/CT. The survival rate was significantly higher in 18F-FDG-PET/CT negative than in positive cases (p = 0.04) [21].

Previous studies examined the effect of post-treatment (from 1 to 109 months after treatment) PET/CT on the prognosis of the disease [22, 24]. Avril et al. found that consecutive 18F-FDG PET/CT has more accuracy than clinical and histopathologic parameters, including changes in CA125 for evaluating the prolonged response to different therapeutic options [23]. Also, Chu et al. reported that the initial post-treatment PET/CT within 3 to 9 months has more sensitivity than CA125 in detecting OC recurrence [22].

This was in the same agreement as our results that showed that PET/CT is the most valuable modality for the long-term follow-up for patients with high or normal CA125, and in patients with negative or inconclusive CT imaging results in terms of local recurrence, peritoneal deposits, suspicious lymph nodes and distant organ metastases.

However, this was in contrast with that of Kurosaki et al. who found that high serum CA125 level may be more beneficial than 18F-FDG-PET/CT imaging in the diagnosis of recurrent OC during the postoperative follow-up periods [24].

Limitations of the study

There was some limitation in our study as it was a retrospective study. It didn’t represent all the population (only included patients who referred to our inistitute). Some cases didn’t have other imaging modalities for comparison. Some cases didn’t follow up for enough period (3 months) and other didn’t come for annual follow-up. Serial measures of CA125 for some patients were not available, we used only the latest CA 125 measure before the PET/CT scan other patient.

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