18FDG PET/CT is a non-invasive imaging modality that evaluates the metabolic activity of tissues and their anatomical details [8].

SUVmax is a semi-quantitative method that reflects the intensity of the 18FDG uptake which is related to the metabolic activity of the cells estimating their behaviour that helps in the diagnosis, staging, and follow-up of various tumors [9].

When compared to primary breast tumors with lower 18F-FDG uptake, tumors with high 18F-FDG uptake had a poor prognosis [10, 11].

Patients with HER2-positive and triple-negative subtype tumors have a higher rate of distant metastasis, local recurrence, and mortality than tumors with luminal A and B subtype-positive tumors [12].

In the literature, multiple studies have reviewed 18F-FDG uptake in patients with breast tumors and related it to histopathological grade, tumor size, and hormone receptor expression as prognostic factors [13,14,15].

Kajáry et al. reported that aggressive tumors (HER2/Neu positive and triple-negative subtype tumors) have high uptake levels of 18F-FDG and higher SUVmax values; as a result, 18F-FDG PET imaging may be useful in predicting disease prognosis [16].

In our study, we used the TLR and TSR as well as the tumor SUVmax. Patients with viable malignant tumors have a higher mean SUV in the liver and spleen as they are organs with increased reticuloendothelial system activity [17].

TLR would provide a proper overview of the tumor metabolic activity and a more accurate diagnostic implementation than SUVmax. Using the TLR obviously remove the SUV limitation such as possible inaccuracies regarding scanner calibration, injected dose, and patient weight index (either actual body weight, lean body mass, or body surface area) [18,19,20].

TLR has been used in multiple new studies to predict axillary lymph node metastasis, evaluate prognosis, and treatment response in locally advanced breast carcinoma [21].

In our study, the mean TLR and TSR had statistically significant relation with the molecular subtype of the breast tumor with P value = 0.018 and 0.061, it was found to be high among the HER2/Neu positive subtype tumors than among triple negative, luminal A and B subtype tumors. This finding agrees with Noda et al. [22] who concluded a positive correlation between tumor to liver SUVmax of the lesion with the molecular subtype (P = 0.0049) and agreed also with AbdElaal et al. [23] who concluded that “the mean TLR values were much higher in Her2neu+, GIII and TN molecular subtype patients (P = 0.002, 0.0476, 0.005 and 0.018 respectively)

In our study we found positive correlation between TLR and TSR and the number of breast lesions (P value = 0.037 and 0.010 respectively), the axillary lymph node activity (P value = 0.048 and 0.041 respectively) and negative correlation between TLR and TSR and size of the axillary lymph nodes (P value = 0.025 and 0.028 respectively), this finding agree with AbdElaal et al. [23] who founded that the median of TLR values was significantly higher in patients with positive axillary lymph nodes (P value = 0.022) and also agree with Önner et al. [14] who founded that the TLR value seems to be more informative than the tumor SUVmax in predicting axillary lymph nodes involvement.

There were a few limitations in our study. First, since this was a retrospective study with a small sample size and was conducted in a single medical center, there was a higher risk of selection bias. More clinical trials with larger sample sizes may be required to confirm our preliminary findings. Second, our study included small tumors which are more susceptible to partial volume effect. Hence, the SUVmax may be underestimated.

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