Radiology: CT lung screening can detect unsuspected malignancies
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| Unenhanced chest CT lung window image reveals that lingula, right middle lobe, and both lower lobes show patchy, peripheral, rounded, peribronchial ground-glass opacities with air bronchograms. Image source: American Journal of Roentgenology |
In addition to examining the lungs, low-dose chest CT studies cover extrapulmonary structures, including the thorax, neck and upper abdomen. The additional range may uncover findings unrelated to the initial purpose of the exam, which may benefit the patient. However, such findings can bring harms in the form of additional costs, patient anxiety and iatrogenic injury for clinically negligible conditions, according to Cristiano Rampinelli, MD, from the department of radiology at European Institute of Oncology in Milan, Italy.
To determine the incidence of extrapulmonary findings during screening CT, Rampinelli and colleagues devised a retrospective analysis of 5,201 patients enrolled in the Continuous Observation of Smoking Subjects (COSMOS) study. COSMOS focused on asymptomatic volunteers, who were current or former heavy smokers (> 20 pack years) and entailed annual screening CT exams beginning in 2004 or 2005.
The researchers extracted all patients with at least one extrapulmonary “potentially significant incidental finding” during the five years of CT screening. They defined such findings as incidentally discovered masses or lesions in the CT study not referable to the lung, bronchial tree or pleura. The study also included all incidental findings detected on PET/CT workups of pulmonary nodules larger than 8 mm.
Rampinelli and colleagues collected all clinically relevant information related to the findings, including diagnostic modality and final diagnosis of the incidental findings, between May and June 2010.
The researchers identified 436 potentially significant incidental findings in 402 subjects and diagnosed 27 unexpected extrapulmonary malignancies by the end of the fifth year of screening. Twenty-four of the patients were alive at the most recent follow-up in September 2010, and 23 of the 24 were disease-free at follow-up.
The most common findings were renal carcinoma, lymphomas and thyroid cancer. Six of the cancers were also detected on PET/CT, which was performed in 248 subjects.
Among the 409 potentially significant incidental findings that did not turn out to be malignant, the diagnostic workup incorporated 303 ultrasound studies, 48 CT studies, 39 PET/CT studies, 20 MR studies, 15 fine needle aspiration biopsies, six endoscopic procedures, five mammograms and one radiographic study.
Rampinelli and colleagues noted that the current study detected a higher rate of extrapulmonary malignancies than previous studies. The incorporation of PET/CT may detect additional malignancies, they said. In addition, repeated annual screening may boost the detection rate because findings missed in one year may be detected in subsequent exams.
“On average, one extrapulmonary malignancy was found for every seven lung cancers diagnosed. This is certainly an important result if we consider that it is unrelated to the primary objective of the low-dose CT examination,” wrote Rampinelli.
Because the most frequent malignancies were renal cancers and lymphomas, the researchers recommended the following low-dose CT reading algorithm: lung evaluation followed by evaluation of the extrapulmonary structures with a soft tissue window, with a careful evaluation of the kidneys and lymph node enlargement.
The researchers suggested that low-dose CT can depict extrapulmonary cancers at an earlier stage, which may enhance the potential value of CT screening for lung cancer. For example, six of the seven renal cancers detected in the study were stage I, which is associated with a 90 percent five-year survival rate. However, in practice, many patients are diagnosed at later stages, with lower survival rates.
Rampinelli et al acknowledged the possibility of overdiagnosis and said that further studies may be required to uncover the true benefit of detection of incidental extrapulmonary malignancies. They also noted that the study did not examine data related to incidental findings not considered to be clinically significant. In addition, it did not incorporate a cost analysis.
The researchers called for further studies to assess the economic and health implications of their findings and emphasized that physicians should evaluate extrapulmonary structures, particularly the kidneys and lymph nodes, when reading lung CT screening studies.