2017 Section 7 Green Book

Clinical Review & Education Review

Use of FDG-PET/CT in Oropharyngeal Squamous Cell Carcinoma

The limitationof PET is in theevaluationof the clinicallyN0neck. Despite PET performing better than conventional imaging in detec- tion of involved LNs in a clinically N0 neck, the results are not optimal. 16 Althoughdifferentstudiesapplieddifferentqualitativefea- tures, different SUV max cutoffs, and different timing for detecting LN involvement, in most studies, the specificity of PET was re- ported between 85% and 90%, whereas the sensitivity was low (50%-70%). 17 Aprevious study reported that whenPET/CTwas ap- plied to distinguish N0 neck from N-positive neck, it had limita- tionsduetothehighnumberoffalse-positivefindings. 18 Ontheother hand, Kovacs et al 19 reported that only 0% to 20%of positive sen- tinel LNs had been diagnosed by PET and this was due to technical limitations, given that micrometastases smaller than 5 mm are be- yond PET’s resolution. The ongoing ACRIN6685multicenter study is investigating the value of PET/CT in clinical evaluation of the N0 neck, and the results of this study will aid in determining the best role for PET/CT in these patients ( Figure 1 ). The most common cause of failure of therapy in patients with OPSCC is undetected distant metastasis. The incidence of distant metastasis in OPSCC is 15% to 20%. Patients with distant metasta- sis from OPSCC usually receive palliative chemotherapy. 20 There- fore, it is important to detect patientswith distantmetastasis in the primary staging evaluation to determine the best strategy of man- agement for them. In multiple previous studies, it has been shown that PET is a good imagingmodality to find distantmetastasis in pa- tientswithOPSCC. 20 In 1 study, the diagnostic capability of PETwas shown to be higher than 3-T whole-body MRI for detecting distant metastasis inOPSCC. 21 The sensitivity and specificitywere92%and 93%, respectively. Therefore, PET scan is recommended as the first imaging modality for detecting distant metastasis in OPSCC 20 ( Figure 2 A and B). Common risk factors such as smoking, as well as genetic predispo- sition, may place patients with head and neck cancer at risk of de- veloping second primary cancers. 22 The chance of developing sec- ond primary cancers in patients with primary head and neck cancer is 10- to 30-fold higher than in the general population. 21 Krabbe et al 23 reported that 10%of patients with oral and oropharyngeal SCC developed second primary cancer in approximately 7 months fol- lowing initial diagnosis. In a larger study of oral and oropharyngeal SCC (917 cases), 16% of patients developed second primary can- cers with 2.6 years median time of diagnosis. The risk of develop- ing a second primary tumor increaseswith longer follow-up regard- less of the patient’s age and sex. 24 Although the sensitivity and specificity of PET/CT in detecting second primary tumors is 100% and 95.7%, respectively, and considerably higher than that of pan- endoscopy, PET/CT is often recommended for diagnosis of second primary cancer only in advanced stages. 25 Value of PET/CT in Detecting Distant Metastasis (M stage) Value of PET/CT in Detecting Second Primary Lesions

Figure 1. Nodal Staging in Patient With Clinically N0 Disease

A

B

tense FDG uptake in OPSCC. However, because the spatial resolu- tion of PET is limited to 5 mm, 12 superficial mucosal lesions may be missed. Also, physiologic FDG uptake of normal oral cavity tissues and oropharyngeal lymphoid tissues (Waldeyer ring) may obscure small tumors. 12 Therefore, some authors claim that PET is inaccu- rate for T1 OPSCC diagnosis but performs well enough in diagnosis of the other stages of OPSCC. 4 Standard uptake value (SUV) is a quantitative parameter of PET that has been performed in evaluation of OPSCC lesions. Metabolic tumor volume (MTV) and total lesion glycolysis (TLG) are other PET parameters that represent volumeofmetabolically active tumor and total activity of the tumor, respectively 13 (eTable 1 in the Supple- ment ). Although multiple studies have assessed the role of these 2 parameters inprognosis ofOPSCC, toour knowledge there is nopub- lished study evaluating the accuracy of theseparameters indiscrimi- natingbenign frommalignant oropharyngeal lesions (eFigure 1 in the Supplement ). Because of high lymphatic drainage, OPSCC has a tendency to me- tastasize early to the cervical lymph nodes (LNs). 14 Accurate staging of OPSCC is the initial step in themanagement of this cancer, andde- tectionof cervical LN involvement plays amajor role in staging. 7 Posi- tron emission tomography has a higher accuracy of detecting cervi- cal LN involvement than CT or MRI, with a sensitivity and specificity of 89% and 81%, respectively. 4 This was verified by a meta-analysis that analyzeddata from32 previous studies that evaluated the accu- racy of PET in cervical LNdetection of head and neck cancers and re- ported79%sensitivityand86%specificity,comparedwithlowerval- ues for CT, MRI, or CT plus MRI (eTable 2 in the Supplement ). 15 hypermetabolic level II (standard uptake value, 5.26) lymph node (arrowhead). The patient was treated with radiation therapy (6000 cGy) and chemotherapy (7 weeks cetuximab), but because of persistent local disease, weekly palliative chemotherapy (weekly docetaxel) was continued. His last follow-up in our center was 7 months after completion of primary treatment. Value of PET/CT in Cervical Lymph Node Metastasis (N stage) Axial fused positron emission tomography/computed tomography images of initial scan of a man in his 60s with a diagnosis of squamous cell carcinoma of the base of the tongue, extending to the soft palate and retromolar trigone on the right side. The 18 F-fludeoxyglucose–positron emission tomography/ computed tomography scan was performed to stage the disease. A, Intense fludeoxyglucose uptake in the oropharyngeal tumor (standard uptake value, 12.83) (arrowhead). B, Intense fludeoxyglucose uptake in 1 ipsilateral

JAMA Otolaryngology–Head & Neck Surgery January 2016 Volume 142, Number 1 (Reprinted)

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