Is PET/CT scan useful in detecting lung metastasis in patients with colorectal cancer?

This study examined the frequency of detecting indeterminate lung lesions on CT of patients with colorectal cancer and investigated if PET/CT was useful in detecting the malignant cases.

Colorectal cancer staging describes the severity of one’s cancer based upon the size and extent of the primary tumor and whether or not cancer has metastasized (spread) into distant organs. One of the common locations of colorectal cancer metastasis is the lungs which can be detected by imaging techniques. It has been shown in studies that early detection and surgical resection of lung metastases can result in a 5-year survival of up to more than 50%.

Computed tomography, or CT scan, generates detailed pictures of structures inside the body and is capable of determining the stage of colorectal cancer. In some cases, indeterminate lung lesions are detected. These lesions are abnormalities in the lung tissue which may develop into malignant tumors. Identifying the tumors’ malignant character requires a positron emission tomography–computed tomography (PET/CT) scan. This scan combines CT and a PET (an imaging technique that uses injected radioactive drug to show cancerous cells in the body) into one scan to provide more detailed information about one’s cancer.

This study investigated the frequency of indeterminate lung lesions on staging CT, the rate of the indeterminate lung lesions being malignant after 24 months and to investigate if PET/CT was beneficial in pointing out the malignant cases.

The present study analyzed the data of 238 patients operated on for colorectal cancer and followed for 24 months. All patients underwent a preoperative CT of the chest and the abdomen in order to stage their disease. Where indeterminate lung lesions were detected, patients had a PET/CT scan performed three months postoperatively and chest CT performed 6, 12, 18 and 24 months postoperatively.

Results showed that during the preoperative CT scan, 47 (20%) patients had indeterminate lung lesions. After 24 months, 8.5% of patients with indeterminate lung lesions had developed lung metastasis which was detected an average of 9 months postoperatively.

185 patients had no indeterminate lung lesions on their preoperative staging CT scan. 5.4% of these patients developed lung metastasis. For these patients, the metastasis was detected at an average of 16 months postoperatively. This was significantly later than in patients with preoperative indeterminate lung lesions. 

Even though a relatively low number of indeterminate lung lesions were cast as malignant, the earlier detection of these lesions and the ability to determine their malignant nature by the use of PET/CT scan in the postoperative follow up period may contribute to patients’ prognosis.

The study included a small number of participants which may have had an implication on the results.

Ask your physician about postoperative CT and PET/CT scan tests.