Circulating tumor cells (CTCs) are cancer cells that are detached from the primary and metastatic tumor site and invade the bloodstream. Most importantly, CTCs are the key players in the development of metastasis. As one of the main components of liquid biopsy, they may significantly contribute to improvements in early cancer diagnosis, monitoring response to therapy, and predicting recurrence of the disease. Although identifying and analyzing CTCs offers the potential for a real-time liquid biopsy, their detection is associated with a number of challenges, which mainly stem from three sources: complexity of the CTCs, complexity of the media (blood), and performance of the detection assays. Particularly, low concentration of the CTCs and the presence of a vast population of hematopoietic cells in the blood make their detection technically complex. The heterogeneity of the target cells and not enough sensitivity of the measuring platforms are also among major technical challenges in CTC detection. Therefore, this review aims to give an update on various methods developed for CTC isolation, including chip-based assays and biosensors. The work will elucidate various challenges associated with the isolation and detection of CTCs and showcase the studies that aimed to tackle them. A number of available commercial platforms for CTC detection and hurdles associated with their widespread applications in clinical settings will also be discussed.

The accuracy and efficacy of medical treatment would be greatly improved by the continuous and real-time monitoring of protein biomarkers. Identification of cancer biomarkers in patients with solid malignant tumors is receiving increasing attention. Existing techniques for detecting cancer proteins, such as the enzyme-linked immunosorbent assay, require a lot of work, are not multiplexed, and only allow for single-time point observations. In order to get one step closer to clinical usage, a dynamic platform for biosensing the cancer biomarker CD44 using a single-mode optical fiber-based ball resonator biosensor was designed, constructed and evaluated in this work. The main novelty of the work is an in-depth study of the capability of an in-house fabricated optical fiber biosensor for in situ detection of a cancer biomarker (CD44 protein) by conducting several types of experiments. The main results of the work are as follows: (1) Calibration of the fabricated fiber-optic ball resonator sensors in both static and dynamic conditions showed similar sensitivity to the refractive index change demonstrating its usefulness as a biosensing platform for dynamic measurements; (2) The fabricated sensors were shown to be insensitive to pressure changes further confirming their utility as an in situ sensor; (3) The sensor’s packaging and placement were optimized to create a better environment for the fabricated ball resonator’s performance in blood-mimicking environment; (4) Incubating increasing protein concentrations with antibody-functionalized sensor resulted in nearly instantaneous signal change indicating a femtomolar detection limit in a dynamic range from 7.1 aM to 16.7 nM; (5) The consistency of the obtained signal change was confirmed by repeatability studies; (6) Specificity experiments conducted under dynamic conditions demonstrated that the biosensors are highly selective to the targeted protein; (7) Surface morphology studies by AFM measurements further confirm the biosensor’s exceptional sensitivity by revealing a considerable shift in height but no change in surface roughness after detection. The biosensor’s ability to analyze clinically relevant proteins in real time with high sensitivity offers an advancement in the detection and monitoring of malignant tumors, hence improving patient diagnosis and health status surveillance.

Optical fiber ball resonators based on single-mode fibers in the infrared range are an emerging technology for refractive index sensing and biosensing. These devices are easy and rapid to fabricate using a CO₂ laser splicer and yield a very low finesse reflection spectrum with a quasi-random pattern. In addition, they can be functionalized for biosensing by using a thin-film sputtering method. A common problem of this type of device is that the spectral response is substantially unknown, and poorly correlated with the size and shape of the spherical device. In this work, we propose a detection method based on Karhunen−Loeve transform (KLT), applied to the undersampled spectrum measured by an optical backscatter reflectometer. We show that this method correctly detects the response of the ball resonator in any working condition, without prior knowledge of the sensor under interrogation. First, this method for refractive index sensing of a gold-coated resonator is applied, showing 1594 RIU⁻¹ sensitivity; then, this concept is extended to a biofunctionalized ball resonator, detecting CD44 cancer biomarker concentration with a picomolar-level limit of detection (19.7 pM) and high specificity (30–41%).

Objective: This umbrella review aims to analyze the effectiveness of exercise therapy for low back pain through an analysis of systematic reviews that evaluate pain reduction, quality of life improvement, and functional outcomes. Methods: This review adhered to PRISMA guidelines and systematic review of review recommendations by searching across PubMed, Scopus, and the Cochrane Library. This study searched for systematic reviews alongside meta-analyses that evaluated exercise interventions in treating low back pain (LBP). This study included reviews that examined exercise therapy for LBP patients and presented data regarding their pain intensity, disability, and quality-of-life outcomes. Data extraction and quality assessment were performed independently by several reviewers. The methodological quality of the included systematic reviews was assessed using the AMSTAR 2 tool. Results: This research yielded 88 systematic reviews from 997 evaluated records. Reduction of pain emerged as the primary measured outcome in systematic reviews (81.8%, n = 72), and these studies showed significant improvement rates of 83.0%. The proportion of studies that concluded no change was 9.1%. The most frequently studied exercises were strengthening, aerobic, and mind–body exercises. The reviews reported quality of life improvements in 27.3% (n = 24), but most reviews (68.2%) did not assess this outcome. No studies indicated worsening outcomes. Exercise interventions demonstrated various forms that effectively contribute to LBP management, according to the study results. Conclusions: This umbrella review of 88 systematic reviews highlights that exercise therapy is a safe, effective, and commonly used strategy for managing low back pain. However, key limitations include the low methodological quality of several included reviews, risk of bias, imprecision, limited reporting of adverse effects, and confounding from multicomponent interventions. While there is limited certainty that any one type of exercise is more effective than others, individualized approaches and patient adherence appear to be critical factors in optimizing outcomes.

The detection of soluble proteins in biological fluids, as a form of liquid biopsy, is a promising tool for cancer diagnosis and prognosis, as it is less invasive than traditional diagnostic methods. CD44 is one of the most recognized markers of cancer stem cells, a small subset of cells responsible for cancer initiation, progression, and metastasis. Given the importance of CD44 as a cancer biomarker, several review articles explore the diagnostic and therapeutic value of cell-surface CD44. In addition to being a membrane-anchored protein, CD44 is also shed from the cell surface and can be found in various biological fluids. However, the role of soluble CD44 in cancer has not been comprehensively discussed in recent reviews. Measuring soluble CD44 in various biological liquids can provide a practical and valuable tool for cancer diagnosis and treatment monitoring. Therefore, this review comprehensively discusses the role of soluble CD44 as a marker in various cancer types, including serum, saliva, urine, and other fluids. In particular, its role as an early cancer biomarker and as a predictive and prognostic biomarker in several cancers is discussed. This work also provides an overview of a wide range of analytical techniques used to detect soluble CD44. The value of cells expressing CD44 versus soluble CD44 as a biomarker is also compared. The review concludes with a perspective on future directions, emphasizing the shift toward non-invasive analytical methods and the need for standardization of detection, including multiple biomarkers during evaluation, to improve the accuracy of cancer diagnosis.