The semiquantitative parameter "standard uptake value" (SUV) of ¹⁸Fluorodeoxyglucose (FDG) positron-emission tomography (PET) provides important additional information about colorectal cancer. In general, colorectal cancers exhibit different growth patterns with different clinicopathological characteristics. The aim of this study was to elucidate the link between the macroscopic appearance of colorectal cancers and maximum SUV (SUV_max) FDG uptakes.

We analyzed 347 patients with colorectal cancer who underwent PET scanning before treatment. The SUV_max of colorectal cancer was analyzed by examining PET images. The macroscopic appearance of each colorectal cancer was classified into three major types: ulcerofungating (n=223), ulceroinfiltrating (n=44), and fungating (n=78). Two cases that were difficult to classify were excluded from the study.

The SUV_max was higher in colorectal cancers with an ulcerofungating appearance (12.19±5.84, mean±standard deviation) and ulceroinfiltrating appearance (11.66±5.63) than in those with a fungating appearance (9.58±6.67; P =0.005) (ulcerofungating and ulceroinfiltrative vs. fungating, P <0.001). A smaller tumor size ( P <0.001) were significantly related to the fungating colorectal cancer. Four out of six colorectal cancers that did not show FDG uptake were the fungating type.

Colorectal cancers with a fungating appearance exhibit a lower SUV_max, shallower invasion and smaller tumor size. Our results indicate that colorectal cancers with a fungating appearance would be less prominent on PET scan than those with an ulcerofungating or ulceroinfiltrating appearance, and thus require more attention.