Case of the Month—November 2004

Detection of Primary Lung Cancer

History
A 60-year-old female presented with multiple bone lesions on her bone scan. A biopsy of the bone lesion revealed metastatic adenocarcinoma. CT of the chest, abdomen, and pelvis were interpreted as unremarkable. A PET scan was requested for evaluation of the primary cancer.

PET Findings
The FDG PET whole-body scan demonstrated multiple foci of intense FDG uptake involving the thoracic and lumbar spine, pelvic bones, right humeral head, and bilateral femora which is consistent with metastatic disease. There was also a focus of FDG uptake seen in the right upper lobe of the lung medially, just adjacent to the spine (Figure 1). This is consistent with primary lung cancer. Retrospectively, it appears that there was a subtle lesion in the right lung adjacent to the spine on the CT scan performed prior to the PET study (Figure 2).

Coronal view

Figure 1.

Transaxial view

Figure 2.

How Did PET Help?
PET helped to identify previously unknown primary cancer in this patient. The result of the PET study changed the patient’s management, since the treatment for metastatic adenocarcinoma from an unknown primary is different from the treatment for metastatic adenocarcinoma where the primary is lung cancer.

Discussion
Metastatic cancer of unknown primary site accounts for about 3% of all malignant neoplasms. The use of PET has resulted in improvements in diagnosis although it has not been approved for routine use in the detection of primary cancer. The most frequently detected primaries are carcinoma hidden in the lung and pancreas (1). Identification and treatment of these patients is of paramount importance.

(1) Pavlidis et al. “Diagnostic and therapeutic management of cancer of an unknown primary.” Eur J Cancer, 2004 June, 40(9): 1454-5.

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