Short summary

Patients with suspected occult cancer (in Danish; mistanke om alvorlig sygdom (MAS)) are increasingly being referred to PET/CT by clinicians from a wide range of specialties. Little is known about the MAS patient group and the research in the topic is scarce. It has not been established if PET/CT beneficial for diagnostic procedure for this specific group of patients. The aim of the study is to describe the patient population and evaluate the use of PET/CT in the diagnosis of these patients.

Rationale

The purpose of this retrospective study is to investigate the prevalence of cancer among patients with non-specific symptoms of cancer who underwent PET/CT on suspicion of occult cancer as well as describing the population characteristics, e.g. age, sex, reason for referral, and final diagnosis.

Furthermore, the study will investigate the predictive values of PET/CT in confirming or refuting the malignancy diagnosis through a follow-up of 1-6 yrs.

Occult cancer/MAS is suspected based on a multitude of vague, non-specific symptoms from several organ systems; such as general malaise, fatigue and large unintended weight loss. The overlap with harmless and self-limiting conditions is great, presenting a challenge to the clinician in distinguishing between malignancy and benign conditions (1). The cancer prevalence in this patient group has previously been found to be between 10-22% (1,2,3,4).

The patient group is heterogeneous and often undergo several, possibly invasive procedures before a diagnosis is obtained. The patient group in which the suspicion is raised is not well described, hence determining the individual risk of illness as well as identifying risk groups is troublesome (2,5). Early detection and localisation of cancer is paramount for the prognosis and treatment of the patient (5). Patients are initially screened with physical examination and laboratory evaluation (step 1), and subsequently CT of the thorax and abdomen (step 2) by the general practitioner (GP) before they are referred to a diagnostic outpatient clinic (DOC). Currently, PET/CT is not standard in the diagnosis of MAS patients at the DOC, but may be ordered at the treating physician's discretion.          

FDG-PET/CT is a relatively novel non-invasive nuclear medicine technology using positron emission tomography (PET) to detect the distribution of positron emitting radioisotopes. The most widely used radiopharmaceutical is fluorine-18-labelled deoxyglucose (FDG). FDG is a glucose analogue that accumulates in cells with high glucose metabolism such as different malignant cells and cells relate to inflammation and infection. In combination with conventional computed tomography (CT), PET/CT allows for location of hypermetabolic foci, including cancers, with high sensitivity and anatomical precision. At present, FDG-PET/CT is used in a multitude of different malignancies for diagnosis, staging, response evaluation, and treatment planning and/or recurrence detection (6). The role of FDG-PET/CT in various cancer diagnostics and staging is well established.  In a selected high-cancer prevalent groups like MAS patients, FDG-PET/CT might shorten time-to-diagnosis as well as effectively refuting a malignancy diagnosis. Although not part of the official guidelines in the diagnostic pathway, FDG- PET/CT is often requested by a variety of specialities when an occult cancer is suspected and it is the ambition of this study to evaluate whether this is a well-suited approach.  

references:

1. Sundhedsstyrelsen. Diagnostisk pakkeforløb for patienter med uspecifikke symptomer på alvorlig sygdom som kunne være kræft. København. 2016
2. Bislev LS, Bruun BJ, Gregersen S, et al. Prevalence of cancer in Danish patients referred to a fast-track diagnostic pathway is substantial. Dan Med J. 2015; 62: A5138
3. Ingeman ML, Christensen MB, Bro F, et al. The Danish cancer pathway for patients with serious non-specific symptom and signs of cancer - a cross-sectional study of patient characteristics and cancer probability. BMC Cancer. 2015; 15:421
4. Lebech AM, Gaardsting A, Loft A, et al. Whole body ¹⁸FDG Pet/CT is superior to CT as first-line diagnostic imaging in patients referred with serious Nonspecific Symptoms or signs of cancer: A randomized prospective study. J Nucl Med. 2017; 58:1058-1064
5. Fredberg U, Vedsted P. Organisation af udredning af patienter med uspecifikke alvorlige symptomer. Ugeskr Læger 2011; 1718-21
6. Hess S, Blomberg BA, Zhu HJ, et al. The pivotal role of FDG-PET/CT in modern medicine. Acad Radiol: 2014; 232-249

Description of the cohort

The study includes all patients that underwent PET/CT at the department of Nuclear Medicine at the Odense University Hospital (OUH) in the period 2010/2011 for suspicion of serious disease (MAS)/occult cancer. 99 patients have been identified.

Data and biological material

Data in the project are register data from the OUH PET/CT database and clinical data collected from the patient medical file. 

Collaborating researchers and departments

Department of Nuclear medicine, OUH Hospital

• Associate professor and Senior consultant Søren Hess
• Consultant Oke Gerke
• Pregraduate student Kamilla Bredlund Caspersen