Breast cancer screening and diagnostic pathways almost exclusively use imaging and tissue biopsy to diagnose breast cancer or to rule it out. Multi-modal testing is the mainstay and has led to overall improvements in testing accuracy. Despite this, currently available options have limitations, necessitating the exploration of alternative approaches. BREASTEST plus is a blood test that was developed using a novel lipidomic platform combined with liquid chromatography tandem mass spectrometry (LC-MS/MS) and machine learning. The assay measures a panel of seven lipids in blood plasma that are converted into a test result by a diagnostic algorithm. This is the first lipidomic clinical assay to be made available commercially for use in oncology. The LC-MS/MS method validation was performed using a SCIEX 6500+ and assessing key parameters such as Linearity, Carryover, Lower and Upper Limits of Quantitation, Imprecision, Specificity, Recovery, Matrix Effects, Interference Studies, Robustness, and Measurement Uncertainty. Sample preparation involved a simple methanolic monophasic extraction for high throughput analyses, and utilised deuterated internal standards for accurate quantitation. The LC-MS/MS method has <6-minute runtime per sample. Detection occurred in electrospray ionisation polarity-switching mode via multiple reaction monitoring (MRM). The method was highly precise, linear and robust. Recovery ranged from 75.0% to 125.0%, with matrix effects mitigated by internal standards. All lipid stability parameters tested passed, and hemolysis and lipemia were noted as sources of interference. A successful interlaboratory comparison has additionally been completed which was crucial for ensuring the accuracy and reliability of the laboratory results. The clinical performance of the assay has been evaluated on prospectively collected plasma samples from Australian women (n=720), validating the suitability of the method, and assay, for routine clinical use.