Elsevier

Clinical Radiology

Volume 64, Issue 7, July 2009, Pages 675-681
Clinical Radiology

Sarcoid-like reaction to malignancy on whole-body integrated 18F-FDG PET/CT: prevalence and disease pattern

https://doi.org/10.1016/j.crad.2009.03.005Get rights and content

Aim

To evaluate the prevalence of sarcoid-like reaction to malignancy detected using integrated 2-[18F]-fluoro-2-deoxy-d-glucose (FDG) positron-emission tomography and computed tomography (PET/CT) in patients undergoing staging or restaging of solid-organ malignancy.

Materials and methods

A systematic search was performed using the institutional radiology information system of 2048 consecutive PET/CT examinations performed in cancer patients at a tertiary-referral centre. Cases that were considered suspicious for sarcoid-like reaction were identified from the initial radiological report and were retrospectively reviewed by three experienced PET/CT reporters.

Results

Sarcoid-like reaction was initially suspected in 23 of the 2048 (1.1%) FDG PET/CT examinations, with the diagnosis confirmed histologically or by clinico-radiological follow-up in 13 of the 23 cases (57%). Sarcoid-like reaction was more commonly seen in patients undergoing FDG PET/CT for restaging of suspected recurrence rather than for primary tumour staging (77% versus 23%; p = 0.05). The mean maximum standardized uptake value (SUVmax) of confirmed hilar and mediastinal sarcoid-like reaction was 7.3 (range 3.1–13.6). Symmetric hilar uptake was demonstrated in 11 of the 13 (85%) and all 13 had additional mediastinal nodal uptake. Pulmonary uptake was seen in seven of the 13 cases (54%). Extra-thoracic involvement was present in eight of the 13 (61.5%), including nodal, splenic, and hepatic lesions.

Conclusion

Sarcoid-like reaction was suspected in 1.1% of cancer patients at FDG PET/CT examination, with confirmation of the diagnosis in 0.6%. With the increasing use of FDG PET/CT in cancer patients, it is important to be aware of the prevalence of this uncommon, but important, disease entity and to consider this diagnosis in appropriate cases in order to avoid a false-positive interpretation of metastatic disease.

Introduction

Sarcoidosis is a systemic inflammatory disease of unknown cause that is characterized by the presence of non-caseating granulomas in affected tissues. The disease has multiple clinical manifestations, ranging from single organ involvement to multisystem disease.1 The link between sarcoidosis and malignancy is a controversial and confusing one, but there is evidence to suggest that such a relationship exists.2, 3 It is recognized that patients with established sarcoidosis have a higher incidence of lung cancer, and it has been shown that patients with sarcoidosis have a more than five-fold increased incidence of haematological malignancy.4 In a process that is often referred to as sarcoid-like reaction, non-caseating granulomas may also develop in patients with underlying cancer,5 and sarcoid-like reactions have been described in association with many different types of solid-organ malignancy.6, 7 With the increasing use of 2-[18F]-fluoro-2-deoxy-d-glucose (FDG) positron-emission tomography (PET) and PET/computed tomography (PET/CT) in cancer patients, it is being recognized that sarcoid-like reaction may result in FDG uptake that needs to be differentiated from tumour recurrence, as described in a few recent case reports.8, 9, 10, 11 This is the first study that describes the prevalence of this entity in cancer patients undergoing FDG PET/CT and analyses the patterns of FDG uptake seen in such cases, whilst emphasizing the importance of recognizing this pattern of abnormality in order to avoid a potential interpretive pitfall that may lead to inappropriate management.

Section snippets

Database search

A retrospective search of our institutional radiology information system (RIS) revealed that 2048 patients had attended FDG PET/CT examinations for staging or restaging of solid-organ malignancy between 1 September 2006 and 30 June 2008. Local ethics committee approval is not required in our institution for retrospective case series reviews. In cases of suspected sarcoid-like reaction identified from the original radiological reports, further information was obtained from the clinical and

Results

Twenty-four of 2048 (1.2%) cases were reported as having sarcoid-like reaction on FDG PET/CT from the original reports on the RIS. One patient was discovered to have known pulmonary sarcoidosis, clinical information that was unavailable to the initial reporter, and this case was excluded from further analysis. The diagnosis was confirmed in 13 of the remaining 23 cases (57%; Fig. 1). Histological confirmation was obtained in 10 of the 13, and clinical confirmation of the diagnosis by

Discussion

The development of non-caseating granulomas in patients with underlying malignancy is often referred to as sarcoid-like reaction, particularly when the patient is asymptomatic.5 It has been estimated that approximately 4–14% of all patients with cancer exhibit histopathological evidence of sarcoid-like reactions,3, 6 and this has been described in association with many tumour types, including haematological, testicular, pulmonary, gastric, colonic, breast, uterine, and sarcomatous neoplasms.3, 5

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