CLN - Bench Matters
Cancer diagnosis and prognosis increasingly relies on the analysis of molecular features from tumor biopsies. Since its first application in tissue sample analysis in 2005, ambient ionization mass spectrometry (MS) has made significant strides, and helped reshape the landscape of intraoperative molecular diagnostics. This article describes the recent advances in intraoperative MS with a focus on ambient ionization techniques and the challenges that need to be addressed for clinical implementation.
Molecular features improve cancer diagnosis and treatment
The predominant method for tumor diagnosis during surgery is based on a technique developed more than 150 years ago — frozen section histopathology. In addition to being time-consuming, the microscopic review of frozen sections is limited insomuch as it is primarily used only to provide an initial diagnosis of tissue biopsies, confirm the nature of the lesion, and ascertain the need for surgical resection. Nonetheless, this method leaves the diagnostic consultation incomplete and, at times, inconclusive in the absence of relevant molecular features. Noninvasive medical imaging methods, although helpful for determining surgical approach and extent of resection, do not allow for the comprehensive analysis of molecular features.
Molecular features of cancer have become significant factors for informing patient prognosis and clinical decision-making. These features often offer more accurate indicators than cellular morphology and imaging alone. Consequently, treatment approaches have shifted from a one-size-fits-all approach towards protocols that are tailored to the unique molecular profile of a patient’s tumor. However, enacting this personalized approach intraoperatively requires an intraoperative assessment of molecular features, which has only recently become possible.
MS enables rapid molecular analysis
There is a clear clinical need for novel technologies that will enable rapid disease diagnosis based on molecular features, ideally from unprocessed samples. MS is a highly sensitive and powerful analytical technique capable of detecting and quantifying diagnostic molecules (specifically metabolites, lipids, and proteins) from complex matrices. Ambient ionization MS provides limits of detection in the sub-parts-per-million range on complex tissue samples. For these reasons, MS tissue analysis methods may be able to provide clinically relevant diagnostic information on biological specimens at the time of surgery. A minimum requirement for surgical relevance is that a technique provides reliable molecular data rapidly while using unprocessed samples. However, intraoperative MS faces barriers to implementation due to the time required for sample preparation and an antiquated imperative to combine separation techniques such as gas chromatography with MS.
Ambient ionization methods take MS to the patient
Ambient ionization methods overcame this barrier to implementation and are well-suited to intraoperative applications due to their ability to generate ions directly, under ambient conditions. This eliminates the need for ionization in a vacuum or for sample pretreatment or purification. The first tissue measurement completed with ambient ionization occurred in 2005 using an electrospray (desorption electrospray ionization). Since then, many ambient ionization methods have been developed, including those using an electrocautery knife, a surgical laser, and a drop of water. These methods differ in the amount of tissue being removed, analysis time, risk of cross-contamination, preanalytical factors, and surface resolution.
Despite variations in their acquisition methods, all these techniques are based on the premise that different types of tissues will exhibit distinct mass spectral profiles. Consequently, the measured profiles can be analyzed and used to differentiate between tissue types, such as distinguishing between cancerous and benign tissue, grades of cancer, and mutation status. In recent studies, researchers have used intraoperative MS methods to characterize tissue samples and differentiate between cancerous and benign material at tumor margins, both in vivo and in vitro.
For example, in brain cancer, metabolic profiling using ambient ionization has identified specific metabolites associated with different cancer types (glioma, lymphoma, meningioma), as well as the presence of prognostic isocitrate dehydrogenase mutations. In ovarian and thyroid cancer, the intensity profile of lipids within tumors has been used to distinguish cancerous margins from neighboring healthy tissue. The implementation of these methods in clinical and surgical settings has the potential to inform clinical decision-making, both intraoperatively and postoperatively, and enhance patient care by improving surgical outcomes, maximizing the extent of resection, reducing operation length, and increasing treatment efficacy.
Pathway to clinical implementation is uncharted, but promising
The path to acceptance of ambient ionization MS as a standard medical tool is not clear. Regulatory hurdles pose challenges, with an unclear path to Food and Drug Administration approval, especially considering the new laboratory developed test rule and limited publication of multicenter studies. Additionally, for results to be acted upon intraoperatively, data processing workflows need to provide validated, actionable results in near-real time, but the regulatory path for integrated diagnostic algorithms remains to be determined. To translate these technologies to routine clinical practice, collaborations among teams with expertise in ambient ionization MS, instrumentation manufacturing, and clinical practice are critical. Medical institutions of all sizes will incorporate this technology to meet a variety of clinical needs, but only with access to commercially approved clinical and surgical instruments.
The potential of ambient ionization MS is high. Intraoperative MS has the potential to reshape the landscape of intraoperative molecular diagnostics. Its inherent strengths make it well-suited to play a significant role as a diagnostic modality that complements the standard of care by providing information on key molecular features currently unavailable intraoperatively. As we navigate the challenges and continue to innovate, the future of cancer diagnostics looks brighter and more precise.
Hannah Brown, PhD, is the clinical and forensic toxicology medical director at Hennepin Healthcare. She recently completed a clinical fellowship in clinical chemistry at Washington University in St. Louis School of Medicine. +Email: [email protected]