Diagnostic accuracy of integrated 18F-FDG PET/CT for restaging patients with malignant germ cell tumours

Objective:

Evaluation of utility of fluorine-18 fludeoxyglucose (¹⁸F-FDG) positron emission tomography/CT (PET/CT) for restaging patients with primary malignant germ cell tumours (GCTs).

Methods:

Data of 92 patients (age, 31.94 ± 10.1 years; male/female, 86/6) with histopathologically confirmed malignant GCTs (gonadal, 88; mediastinal, 4; seminomatous, 47 and non-seminomatous, 45) who underwent ¹⁸F-FDG PET/CT for restaging (suspected recurrence/post-therapy evaluation) were retrospectively analysed. Two experienced nuclear medicine physicians reviewed the PET/CT images in consensus, qualitatively and semi-quantitatively [maximum standardized uptake value (SUVmax)]. Histopathology (if available) and clinical/imaging/biochemical follow-up (minimum of 6 months) were employed as the reference standard.

Results:

¹⁸F-FDG PET/CT was interpreted as positive in 59 and negative in 33 patients. Local disease was seen in 5, nodal disease in 50 and distant metastasis in 22 patients. PET/CT was true positive in 49, false positive in 10, true negative in 30 and false negative in 3 patients. ¹⁸F-FDG PET/CT showed sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 94.2%, 75.0%, 83.0%, 90.9% and 85.8% overall; 90.0%, 74.0%, 72.0%, 90.9% and 80.8% in seminomatous GCT; and 96.8%, 76.9%, 91.1%, 90.9% and 91.1% in non-seminomatous GCT, respectively. Difference in PET/CT accuracy for seminomatous and non-seminomatous GCTs was not significant (p = 0.263). PET/CT demonstrated disease in 13 patients with negative/equivocal conventional imaging findings and in 9 patients with normal tumour markers. No site- or histology-based difference was seen in SUVmax.

Conclusion:

¹⁸F-FDG PET/CT demonstrates high diagnostic accuracy for restaging patients with malignant GCTs. It has comparable diagnostic performance in both seminomatous and non-seminomatous malignant GCTs.

Advances in knowledge:

The present article demonstrates high diagnostic accuracy of ¹⁸F-FDG PET/CT for restaging both seminomatous and non-seminomatous malignant GCTs in a large patient population.Germ cell tumour (GCT) is the commonest malignancy in males aged between 20 and 35 years.¹ With cisplatin-based chemotherapy, high long-term cure rates can be achieved in patients with GCTs.² Traditionally, the follow-up of patients with GCT is carried out with clinical examination, measurement of serum tumour markers [alpha-fetoprotein (AFP), beta-human chorionic gonadotropin (β-HCG) and lactate dehydrogenase (LDH)], and with conventional imaging investigations such as CT or MRI.³ A major issue in the management of GCTs is post-chemotherapy residual masses, which harbour viable tumour cells in about 11–37% of cases.⁴ Unfortunately, CT or MRI cannot predict the histology of residual masses and has limited specificity in post-therapy setting.⁵Fluorine-18 fludeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) improves the visualization of tumour cells by imaging their upregulated glucose metabolism. Based on this unique feature, ¹⁸F-FDG PET improves the differentiation of viable tumour from non-viable tissue.⁶ In many previous studies, ¹⁸F-FDG PET had been evaluated in patients with seminomatous and non-seminomatous GCTs with post-chemotherapy residual masses, demonstrating promising but variable results.^7–12 However, these studies had mostly employed PET alone, which suffers the limitations of having a lack of anatomical correlation, especially for detection of abdominopelvic disease, which can be overcome by the use of integrated PET/CT.¹³ Since few studies are available regarding the utility of integrated PET/CT in restaging of patients with GCTs, in the present study, this issue has been addressed. Also, since the utility of ¹⁸F-FDG PET/CT is limited for benign GCTs,¹¹ we only included patients with malignant GCTs in the present study.