OBJECTIVE: The tryptophan pathway has been demonstrated to be involved in tumor progression. Increased expression of indoleamine 2,3-dioxygenases has been observed in several human tumors types, such as breast cancer. In order to study the role of IDO expression as a prognostic marker, the serum tryptophan, kynurenine concentrations and the ratio of kynurenine to tryptophan (K/T) of 165 subjects were compared, and correlations were established.

PATIENTS AND METHODS: This is a case-control study involving 39 patients with invasive ductal breast carcinoma. The recruitment period was from January 2018 to December 2019. We investigated the serum tryptophan and kynurenine levels based on liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS: Our analysis shows a faster tryptophan degradation in larger tumors. The K/T ratio was significantly associated with breast cancer risk factors (age, tumor size and biomarkers). It was also significantly associated with KI67 (r=0.208; p=0.007) and with age
(r= 0,166 p=0,033) as well. The plasmatic K/T ratio expression greater than 8.4 μmol/ μmol was significantly associated with an age of 63±14 years old (OR=1.05, 95% IC 1.01-1.09, p=0.02). Regression analysis also shows that higher plasmatic K/T ratio expression was associated two times with higher tumour size and SBR grade (OR=2.11, 95% IC 0.95-2.83, p=0.035; OR=2, 95% IC 1.11-3.54, p=0.02, respectively). Subjects with a high K/T ratio high (>6.2) are associated five times with RE+ and RP+ compared to subjects with a low K/T ratio (<4.2) (OR=5, 95% IC 1.23-18.81, p=0.02; OR=4.2, 95% IC 1.07-16.72, p=0.04, respectively). It was also significantly associated with higher KI67 expression (ki67≥20) (OR=1.14, 95% IC 1.04-1.26, p=0.008).

CONCLUSIONS: The K/T ratio can be used as a new prognostic biomarker for the progression and invasiveness of breast invasive ductal carcinoma.