The Clinical Role Of ¹⁸F-FDG PET/CT In Identifying The Primary Tumors Of Metastases

Objective The malignant tumor is a hazardous disease since it devastates patients' health seriously and damages the quality of their lives.The outstanding feature of malignancy is invasive and metastases.In clinical practice,it is not uncommon that the patients who suffer from prominent symptom of metastases but with occult primary malignancy.However,in some cases,conventional imaging is difficult in differentiating metastases from benign and primary disease.Defined primary tumors plays a key role in guiding the clinician to make suitable therapeutic strategy in the following management.Some reports have indicated that ¹⁸F-FDG PET/CT has its value in seeking primary tumors in the cases of unknown primary.This investigation explores the use of whole-body ¹⁸F-FDG PET/CT in the patients with different sites of metastatic lesions and evaluates its clinical role in identifying the primary malignancy and assesses its accuracy of differentiating metastases from other lesions.Materials and Methods The enrolled subjects were 125 patients(72 males,53 females;mean age,56.4±28.6y).Based on the location of metastatic lesions,they were divided into seven groups.From Groupâ… toâ…¦,patients suffered from metastatic lesions in lymph nodes(n=40),bones(n=33),brains(n=23),livers(n=11), lungs(n=7),adrenal glands(n=5),and others(n=6).Fifty-six of all were confirmed by pathological diagnosis.Data of PET scan were reconstructed and fused with CT slices. PET,CT and fusion images were displayed in three orthogonal projections.Images were interpreted on the Xeleris workstation.All of the PET images were reviewed visually and semi-quantitatively with Standardized Uptake Value.PET images were reviewed in conjunction with relevant the CT and the fused images.The diagnosis for the primary tumor was established according to the appearance of lesion and patients' clinical information.The PET/CT impression was verified by histopathology, conventional imaging modalities and clinical follow-up.To calculate the sensitivity, specificity and accuracy of PET/CT in identifying the primary diseases.Results In 125 patients,primary tumors of 89 patients were confirmed by pathological or clinical follow-up.There were lung cancers(n=42),digestive system carcinomas(n=26),head and neck malignancies(n=10),gynecologic malignancies (n=7),urinary malignancies(n=4).In digestive system carcinomas,there were colon cancers(n=12),gastric cancers(n=5),hepatic cancers(n=3),pancreas cancers(n=3), small intestine cancers(n=2),and esophagus cancers(n=1).In head and neck malignancies,there were nasopharynx cancers(n=3),thyroid cancers(n=2), oropharynx carcinoma(n=1),larynx cancer(n=1),salivary malignant tumor(n=1), maxillary sinus carcinoma(n=1),and carcinoma of fossa orbitalis(n=1).In gynecologic malignancies,there were breast cancers(n=3),ovarian cancers(n=2), cervix cancer(n=1),and uterus leiomyosarcoma(n=1).In urinary malignancies,there were renal cell carcinoma(n=3),prostatic carcinoma(n=3).Eighty-three patients were diagnosed by PET/CT precisely and 6 were misinterpreted.Thirty-six of 125 patients were failed to define the primary tumor and divided into the following categories.Among them,twenty cases suspected metastatic lesions previously were demonstrated as primary disease or parts of it,including intracranial tumors(n=6),malignant lymphoma(n=6),multiple myeloma(n=5),primary adrenal lymphoma(n=2),and malignant fibrous histiocytoma of bone(n=1).Five cases were proved to be benign diseases,including cerebral infarction,adrenal tuberculosis,liver tuberculosis,lung and thyroid benign disease.Eight cases survived in disease-free stage after the clinical follow-up for more than 12 months.In three cases,only metastatic lesions were detected,whose primary tumors had not been determined after at least 12 months clinical follow-up.In above 36 patients,thirty-four were defined by PET/CT accurately and 2 were misinterpreted.The sensitivity,specificity,accuracy,PPV and NPV of PET/CT in identifing primary tumors were 93.26%,94.44%,93.60%,97.65%and 85.00%,respectively. After ¹⁸F-FDG PET/CT examination,27 patients were detected additional metastatic lesions which were missed previously.Conclusion ¹⁸F-FDG PET/CT had shown its promising clinical value in the patients with metastases.It was capable of identifying the primary tumor in the patients with various metastases,and was able to determine the extension of the disease in a single scan.¹⁸F-FDG PET/CT was also illustrated high accuracy in differentiating metastases from other diseases.However,other clinical information including conventional imaging should also be investigated to reduce the number of false-positive and false-negative cases.