Metabolic Imaging Parameters of ¹⁸F FDG PET/CT in Differentiating the Ki-67 Index in Carcinoma Breast

The proliferation index (Ki-67 index) is a known independent prognostic marker in carcinoma breast, and its expression is directly proportional to higher recurrence and worse prognosis. However, there is no standard cutoff of the Ki-67 index to determine its low or high expression. In this study, we aim to find the association of various metabolic parameters on ¹⁸F FDG positron emission tomography/computed tomography (PET/CT) with Ki-67 index in carcinoma breast patients and further evaluate its correlation with low and high Ki-67 index groups.

This is a retrospective study conducted in a tertiary hospital in North India between February 2021 and 2024. All histopathologically proven female cases of carcinoma breast with reported Ki-67 index and baseline ¹⁸F FDG PET/CT before any treatment or surgery were included. The metabolic parameters, namely, standardized uptake value (SUVmax), the metabolic ratio of the primary tumor to the liver (SUR), total lesion glycolysis (TLG), and metabolic tumor volume (MTV) were recorded for each case. The correlation between the metabolic parameters and the Ki-67 index was analyzed, and subgroup analysis was done.

Sixty-five female patients met the inclusion criteria, and the majority of them presented with intraductal carcinoma. The median value (interquartile range [IQR]) of the Ki-67 index was 40% (IQR: 50%). The primary breast tumor showed median (IQR) of SUVmax, SUR, TLG, and MTV of 10.3 g/mL (7.2), 3.7 (2.9), 102.9 g.cub/mL (184.7), and 16.2 cm³ (25.4), respectively. A significant correlation was noted between all the metabolic parameters studied and the Ki-67 index. In subgroup analysis, a significant difference was noted in all the metabolic parameters between the subgroups of the Ki-67 index ≤25% versus >25%.

Metabolic parameters on ¹⁸F FDG PET/CT show a promising role in the determination of the status of proliferation marker Ki-67 index in carcinoma breast.