Pink-color sign in esophageal squamous neoplasia, and speculation regarding the underlying mechanism.

AIM: To investigate the reasons for the occurrence of the pink-color sign of iodine-unstained lesions.
METHODS: In chromoendoscopy, the pink-color sign of iodine-unstained lesions is recognized as useful for the diagnosis of esophageal squamous cell carcinoma. Patients with superficial esophageal neoplasms treated by endoscopic resection were included in the study. Areas of mucosa with and without the pink-color sign were evaluated histologically. The following histologic features that were possibly associated with the pink-color sign were evaluated. The keratinous layer and basal cell layer were classified as present or absent. Cellular atypia was classified as high grade, moderate grade or low grade, based on nuclear irregularity, mitotic figures, loss of polarity, chromatin pattern and nuclear/cytoplasmic ratio. Vascular change was assessed based on dilatation, tortuosity, caliber change and variability in shape. Vessels with these four findings were classified as positive for vascular change. Endoscopic images of the lesions were captured immediately after iodine staining, 2-3 min after iodine staining and after complete fading of iodine staining. Quantitative analysis of color changes after iodine staining was also performed.
RESULTS: A total of 61 superficial esophageal neoplasms in 54 patients were included in the study. The lesions were located in the cervical esophagus in one case, the upper thoracic esophagus in 10 cases, the mid-thoracic esophagus in 33 cases, and the lower thoracic esophagus in 17 cases. The median diameter of the lesions was 20 mm (range: 2-74 mm). Of the 61 lesions, 28 were classified as pink-color sign positive and 33 as pink-color sign negative. The histologic diagnosis was high-grade intraepithelial neoplasia (HGIN) or cancer invading into the lamina propria in 26 of the 28 pink-color sign positive lesions. There was a significant association between pink-color sign positive epithelium and HGIN or invasive cancer (P = 0.0001). Univariate analyses found that absence of the keratinous layer and cellular atypia were significantly associated with the pink-color sign. After Bonferroni correction, there were no significant associations between the pink-color sign and presence of the basal membrane or vascular change. Multivariate analyses found that only absence of the keratinous layer was independently associated with the pink-color sign (OR = 58.8, 95%CI: 5.5-632). Quantitative analysis was performed on 10 superficial esophageal neoplasms with both pink-color sign positive and negative areas in 10 patients. Pink-color sign positive mucosa had a lower mean color value in the late phase (pinkish color) than in the early phase (yellowish color), and had similar mean color values in the late and final phases. These findings suggest that pink-color positive mucosa underwent color fading from the color of the iodine (yellow) to the color of the mucosa (pink) within 2-3 min after iodine staining. Pink-color sign negative mucosa had similar mean color values in the late and early phases (yellowish color), and had a lower mean color value in the final phase (pinkish color) than in the late phase. These findings suggest that pink-color sign negative mucosa did not undergo color fading during the 2-3 min after iodine staining, and underwent color fading only after spraying of sodium thiosulfate.
CONCLUSION: The pink-color sign was associated with absence of the keratinous layer. This sign may be caused by early fading of iodine staining.