View Abstract

A4126 - Diagnostic Process of a Patient with FDG PET Negative Pulmonary Metastases and Prostate Adenocarcinoma
Author Block: K. Eu1, C. V. Choong1, Z. Ng2, J. A. Abisheganaden1; 1Respiratory Medicine, Tan Tock Seng Hospital, Singapore, Singapore, 2Tan Tock Seng Hospital, Singapore, Singapore.
INTRODUCTION
The etiology of multiple pulmonary nodules is far ranging. Differentials include malignancy, benign etiologies such as infections, inflammatory conditions such as granulomatosis with polyangiitis, pulmonary arteriovenous malformations, pneumoconioses.
CASE DESCRIPTION
A 78 year old with incidental left middle zone nodular opacity in chest x-ray was referred to our institution. Computed tomography (CT) scan showed scattered pulmonary nodules bilaterally measuring up to 1.5 x 1.1cm with areas of focal pleural thickening, and no lymphadenopathy. F-18 Fluorodeoxyglucose (FDG) positron emission tomography (PET) did not show FDG uptake in bilateral pulmonary nodules, and no FDG avid nodes. There was mild FDG uptake seen in several bones (SUVmax 3.0).
Plans for histopathological evaluation were not ideal - radiologically guided lung biopsy had bleeding risk, an alternative was wedge resection of the lung, both options which were declined by patient. Nocturia was elucidated on further history. Physical examination found hard, nodular, enlarged prostate. Prostate surface antigen level was markedly elevated at 319 ug/L. Patient subsequently underwent transrectal ultrasound prostate biopsy, histology revealed acinar adenocarcinoma (Gleason 4+4).
DISCUSSION
Differentiation between malignant and benign pulmonary nodules is a frequently encountered problem. Metabolic imaging with PET scan can be used as a diagnostic test to further risk stratify patients. The sensitivity and specificity of PET for identifying malignancy is estimated to be approximately 87% and 83% respectively. Those with negative PET and low pretest probability of cancer can often be managed with a strategy of observation. However, tumours with low activity and small size are known to result in false negatives.
Current literature seems to suggest that pulmonary metastases tend to be FDG avid. A study that retrospectively evaluated prostate cancer patients with lung lesions reported a SUV of 4.4 ± 3.9 for pulmonary metastases, similar to primary lung cancer. Another case report found pulmonary metastases discovered from FDG avid lesions on PET scan. On the contrary, our patient’s pulmonary metastases had low FDG avidity despite its size and advanced stage. False negative pulmonary metastases from prostate cancer does not appear reported thus far.
Our case illustrates the importance of a careful history-taking and physical examination in tracing the primary of our patient’s malignancy. While PET CT scan is a useful tool in the work up of indeterminate lung nodules, awareness of its pitfalls is crucial, and pulmonary metastases from prostate cancer could be considered in the differential of PET negative lung nodules.