FDG PET/ CT is more likely to detect the primary source of the Cancer of unknown primary when presented with cervical lymph nodes metastasis

Introduction: Cancer of unknown primary (CUP) is a cancer with undiscovered primary source.

To check the efficacy of FDG PET / CT for the identification of the primary lesions of CUP in a relatively large group of patients.

Methods: Two hundreds eighty seven cases of CUP that were referred for FDG PET/CT between 2008-2018 at Osaka University Hospital, Japan.

Results: Detection rate for primary lesion of the CUP that presented with neck LN metastases was 40%. Neck LN metastases were the initial presentation in 25% of the CUP cases. The location of the primary tumor was also in the neck area in 82% of the detected primary cancer with cervical metastases presentation. While the primary source of 18% of the detected primaries that presented with neck LN metastases, were located in extra cervical areas. Waldeyer ring was the most common primary source of CUP in the neck; 50%, and 15% were at the larynx. 75% of the CUP cases presented by extra cervical metastases, detection rate was 11%. Lung was the most common primary source; 21%, then the stomach; 13% .

Conclusions: The primary source of CUP presented with cervical LN metastasis is more likely to be detected by FDG PET/ CT, more than those with non cervical LN metastasis. Waldeyer ring is the most common primary source of CUP in the neck.