Association of Standardized Uptake Values of Primary Breast Cancer on [18F]FDG PET/CT With Immunohistochemistry and Molecular Subtypes

The prognostic factors for breast cancer include pre-treatment staging, nodal and distant metastasis, hormone receptor status, ki67 index, and molecular subtype. For adequate treatment, [18F]FDG PET/CT is now being used to prognosticate the course and response of treatment in breast cancer patients. Our study aims to find the association between the metabolic activity of primary breast tumors as PET/CT SUV uptake and prognostic factors such as ER/PgR/Her2neu receptor status, molecular subtypes, ki67 labelling index, and nodal/distant metastasis.

A retrospective observational study at our tertiary care institute included 228 breast cancer patients from March 2017 to April 2021. Pre-treatment PET/CT imaging was done. The immunohistochemical analysis was performed on a biopsy/surgical specimen to determine the molecular subtype of breast cancer. Further, statistical analysis was performed to find the association between PET/CT findings with immunohistochemistry and, thus, molecular subtypes of breast cancers.

Significantly higher SUV max was seen in tumors with ER-negative (Mean SUVmax-11.6; P-value=0.002), PgR negative (Mean SUVmax-11.1; p value-0.0005), triple-negative receptor status (Mean SUVmax-13.7; P-value=0.004) and high Ki67 index (P-value=<0.01). Further Luminal A (Mean SUV max:6.0±5.5 & Median SUV max:3.9±3.6) and Luminal B (Mean SUV max: 8.9±4.9 & Median SUV max:7.6±4.0) subtypes showed lower SUV max as compared to Her2neu (Mean SUV max: 9.4±5.5 & Median SUV max:8.6±6.2) and TNBC (Mean SUV max: 13.7±12.4 & Median SUV max:10.0±7.6) subtypes. However, only a weak correlation was found for axillary nodal spread p-value – 0.02) and no significant correlation was seen for Her2 receptor status (Mean SUVmax-9.7; p value-0.178) and distant metastasis (P-value=0.26).

The values for different molecular subtypes can be used as Mean SUV or Median SUV uptake. However, owing to data skewing in practical scenarios, we suggest the use of median values with interquartile range for predicting the molecular subtypes of breast cancer on PET/CT imaging: Luminal A – Median SUV – 3.9 (IQR – 3.6); Luminal B – Median SUV – 7.6 (IQR – 4.0); Her2neu Enriched – Median SUV 8.6 (IQR - 6.2); Triple-negative breast cancer - Median SUV 10.0 (IQR - 7.6).