CT-guided fine-needle aspiration cytology and CDX2 immunostaining of pulmonary nodules in patients with colorectal cancer.

BACKGROUND: Colorectal cancer (CRC) is the second most common cause of cancer death. The 5-year survival rate varies widely according to the stage of the disease, ranging from 80% to 60% in patients with localized and regional disease, respectively. Unfortunately, 20-25% of patients initially considered free of regional lymph-node involvement, present occult nodal metastases. Similarly, despite the use of CT-scan of the thorax with intravenous contrast with Hounsfield Units measurement and 18F-FDG-PET or PET/CT, more than 20% of metastatic nodules are not detectable preoperatively. Moreover, false-positive images of lung metastases (LM) from CRC are not infrequent, especially in patients at risk of lung cancer. Several alternative strategies have been suggested, enclosed radiotracer-guided biopsy and image-guided navigation. However, the routinely use of CT-guided fine-needle aspiration cytology (FNAC) represents the most sensitive diagnostic tool, especially when immunohistochemical staining of smears is performed. The aim of this study was to evaluate the usefulness of image-guided FNAC in patients with CRC who had undergone colonic resection and developed suspicious pulmonary nodules during follow-up. PATIENTS & METHODS: We studied a group of 12 patients (8 men, 4 women, median age 65 years, range 48-73 years) with primary CRC who underwent routine postoperative staging CT-scan of the liver and the thorax and MRI scan of the pelvis in case of rectal cancer. All the patients showed one or two suspicious pulmonary nodules, and had specific risk factors for another primary cancer, such as smoking history or dangerous chronic chemical substances exposure, with the aim of determining the tissue origin. They underwent CT- guided FNAC for standard cytological evaluation, and immunohistochemical staining for both thyroid transcription factor 1 (TTF1) and caudal type homeobox transcription factor 2 (CDX2), using anti-TTF1 (clone SPT 249) and anti-CDX2 (clone CDX2-88) monoclonal antibodies. RESULTS: TTF1 was positive in 5 specimens (CRC=2, LC=3), while CDX2 was positive in 11 specimens (CRC=10, LC=1). Thus, the sensitivity and positive predictive value (PPV) were 75.0% and 60.0%, and 83.3% and 90.9% for TTF1 and CDX2, respectively (χ2= 4.75, p=0.11). TTF1 and CDX2 together were 100% sensitive (χ2=11.11, p=0.001). IN CONCLUSION, CT-guided FNAC and TTF1+CDX2 immunostaining in combination have a high sensitivity in differentiating between LMs from CRC and other malignancies such as lung cancer. It should be suggested in all patients with CRC and suspicious pulmonary nodules revealed during follow-up.