The presentation of malignant tumours and pre-malignant lesions incidentally found on PET-CT.
OBJECTIVE
The purpose of the study was to determine the general and organ-specific presentation of incidental primary tumours on PET-CT.


METHODS
PET-CT reports of 2,360 consecutive patients were reviewed and revealed 156 lesions suspicious for a new unexpected malignancy, in 151 patients. One hundred and twenty of these lesions, in 115 patients, were further assessed, by biopsy (n=84 patients) or by clinical and imaging follow-up (n=31 patients) for a mean of 17+/-4 months (range 12-25 months).


RESULTS
Forty-four unexpected malignancies were found in 41 of the study patients (1.7%). Twenty-seven of the 44 incidental tumours were identified on the basis of their location, which was uncommon for metastasis of the known malignancy. Eight were detected as a result of either the difference in FDG avidity of the known malignancy and the incidental lesion or the presence of an incidental non-FDG-avid mass on the CT part of the study. Four tumours were synchronous carcinomas in patients with known colorectal malignancy, three were identified by virtue of the discordant response to treatment compared with the known primary tumour and two were detected as new sites of disease after a prolonged disease-free period. There was organ variability in the positive predictive values (PPV) of PET-CT findings for incidental primary malignancy or pre-malignant lesions: 62% for colonic lesions, 54% for lung lesions and 24% for thyroid lesions.


CONCLUSIONS
Incidental primary tumours may be identified on PET-CT based on their location, FDG avidity, response to therapy and time of appearance. The PET and CT parts of the study appear to complement each other and assist in identification of these incidental tumours.
Department of Nuclear Medicine, Tel Aviv Sourasky Medical Center, 6 Weizman Street, Tel Aviv, 64239, Israel. evensap@tasmc.health.gov.il
Einat
E
Even-Sapir
Hedva
H
Lerman
Mordechai
M
Gutman
Gennady
G
Lievshitz
Limor
L
Zuriel
Aaron
A
Polliack
Moshe
M
Inbar
Ur
U
Metser
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D033162:Incidental Findings; D007557:Israel / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000175:diagnosis* / Q000453:epidemiology*; D049268:Positron-Emission Tomography / Q000706:statistics & numerical data*; D011230:Precancerous Conditions / Q000175:diagnosis* / Q000453:epidemiology*; D015995:Prevalence; D015203:Reproducibility of Results; D012189:Retrospective Studies; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D012680:Sensitivity and Specificity; D013382:Subtraction Technique / Q000706:statistics & numerical data; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*