"Pink Pattern" Visualized in Magnifying Endoscopy With Narrow-Band Imaging Is a Novel Feature of Early Differentiated Gastric Cancer: A Bridge Between Endoscopic Images and Histopathological Changes

Abstract

Background: A pink color change occasionally found by us under magnifying endoscopy with narrow-band imaging (ME-NBI) may be a special feature of early gastric cancer (EGC), and was designated the "pink pattern". The purposes of this study were to determine the relationship between the pink pattern and the cytopathological changes in gastric cancer cells and whether the pink pattern is useful for the diagnosis of EGC. Methods: The color features of ME-NBI images and pathological images of cancerous gastric mucosal surfaces were extracted and quantified. The cosine similarity was calculated to evaluate the correlation between the pink pattern and the nucleus-to-cytoplasm ratio of cancerous epithelial cells. Two diagnostic tests were performed by 12 endoscopists using stored ME-NBI images of 185 gastric lesions to investigate the diagnostic efficacy of the pink pattern for EGC. The diagnostic values, such as the area under the curve (AUC), the accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), of test 1 and test 2 were compared. Results: The cosine similarity between the color values of ME-NBI images and pathological images of 20 lesions was at least 0.744. The median AUC, accuracy, sensitivity, specificity, PPV, and NPV of test 2 were significantly better than those of test 1 for all endoscopists and for the junior and experienced groups. Conclusions: The pink pattern observed in ME-NBI images correlated strongly with the change in the nucleus-to-cytoplasm ratio of gastric epithelial cells, and could be considered a useful marker for the diagnosis of differentiated EGC.

Keywords: early gastric cancer; histopathological changes; magnifying endoscopy; pink pattern; vessel-plus-surface classification system.

Figure 1

Representative case of the “pink pattern” when the demarcation line (DL) is indeterminate. (A) Suspected lesion of early cancer in the gastric antrum (dotted boxed area). Left panel shows the conventional white light imaging findings and the right panel shows the narrow-band imaging findings. (B) Magnified image of the dotted boxed area in (A). DL is indeterminate. (C) Magnified image of the dotted boxed area in (B). “Pink pattern” is observed in the lesion (within the yellow dotted line).

Figure 2

Histopathological findings of Figure 1 under different magnification. (A–C) Hematoxylin and eosin staining of the resected specimen showed that the histopathological diagnosis was gastric cancer. Color of the gastric epithelial cells to the left of the red line was much darker than that to the right of the red line. (B) Magnified image of the dotted boxed area in (A). (C) Magnified image of the dotted boxed area in (B). The nucleus-to-cytoplasm ratio of epithelial cells to the left of the red line was higher that of cells to the right of the red line.

Figure 3

Flow chart of this study.

Figure 4

Endoscopic image processing and color feature extraction were performed with Python.

Figure 5

Pathological image processing and color feature extraction were performed with Python.

Figure 6

Similarity evaluation of the trends in color curves for endoscopic images and pathological images. (A) The length of the endoscopic saturation value list is n, the length of the pathological gray value list is m, and the sampling step length is calculated as: L = m/n. List of gray values for the pathological image is averagely sampled by using the step length of L, and the pathological image gray value list with length n was obtained. (B) The length between endoscopic image saturation value list and pathological image gray value list is consistent. (C) Cosine values and color curves for the endoscopic and pathological images are summarized in one figure.

Figure 7

Comparison of diagnostic performances of tests 1 and 2 by all endoscopists (A), junior group (B), and experienced group (C). AUC, area under curve; PPV, positive predictive value; NPV, negative predictive value. P-values were calculated with the Mann–Whitney U test. ^*P < 0.05, ^**P < 0.01, and ^***P < 0.001.

Figure 8

A provisional strategy for gastric cancer diagnosis using the “pink pattern” to supplement to the VS classification system. C-WIL, conventional white light imaging; ME-NBI, magnifying endoscopy with narrow-band imaging; DL, demarcation line; IMVP, irregular microvascular pattern; IMSP, irregular microsurface pattern.