Background: Cancer/testis antigen (CTA) is a class of antigen molecules expressed only in the germinal epithelium of testis and some tumor tissues. As an important CTA molecule, the expression of F-box protein 39 (FBXO39) in breast cancer (BC) and its clinical significance remain unclear. The objective of this study is to explore the value of FBXO39 in the diagnosis, efficacy monitoring, and prognostic evaluation of BC.
Methods: The expression of FBXO39 mRNA in the serum exosomes of patients with BC before and after the initial diagnosis and treatment was detected by qRT-PCR, and the corresponding ROC curve was plotted. The expression of FBXO39 protein in BC cancer tissues was detected by immunohistochemistry, along with the analysis of the correlation between FBXO39 expression and clinical pathological features as well as prognosis of BC cases.
Results: The serum-derived exosomes were successfully isolated and identified. The positive rate of FBXO39 mRNA in serum exosomes of patients with BC was up to 86%; there was a correlation between the expression level of serum exosomal FBXO39 and clinical staging, HER2, and Ki-67 expression (all with p < 0.05). The sensitivity of serum exosomal FBXO39 in distinguishing BC patients from healthy controls was 88%, with the specificity as 86%, and AUC as 0.9432. The expression change of FBXO39 in serum-sourced exosomes of patients with BC was related to their treatment situation, indicating that the level of FBXO39 decreased significantly after treatment. The expression of FBXO39 in cancer tissue was related to the clinical stage (p = 0.023) and lymphatic metastasis (p = 0.015) of the BC patients. Survival analysis showed that the expression of FBXO39 was negatively correlated with the prognosis of BC patients, with the high expression of FBXO39 indicating poor prognosis.
Conclusions: Serum-derived exosomal FBXO39 could serve as an important indicator of BC diagnosis and efficacy evaluation; FBXO39 could be rated as an important indicator of BC prognosis evaluation.