ddPCR has become increasingly important in cancer research, particularly in the study of solid tumors. This highly sensitive technology is instrumental in the detection and quantification of ctDNA, offering researchers and clinicians a powerful tool for non-invasive cancer monitoring by analyzing ctDNA in a patient's blood [4]. ddPCR provides insights into the genetic makeup of tumors and helps in detecting early signs of cancer recurrence or progression. This capability has significant implications for early diagnosis and monitoring of minimal residual disease (MRD) after treatment [5]. ddPCR detects the progression of the disease and MRD in individuals with chronic myeloid leukemia (CML). When it comes to identifying low amounts of BCR/ABL(P210) transcripts, a marker of CML, ddPCR is a more sensitive technique than conventional RT-qPCR. According to the study, RT-qPCR only identified MRD in five of the 61 CML patients, whereas ddPCR was able to identify MRD in 11 of them. Additionally, in four out of ten CML patients that were monitored, ddPCR was able to identify disease progression before RT-qPCR. According to these findings, ddPCR provides a more precise and sensitive way to track MRD and the course of the disease in CML patients [6]. Study done by Guerrini et. Al. found that ddPCR outperformed traditional RT-qPCR in detecting the B-RAF V600E mutation, identifying it in more patients and earlier in disease progression. These results highlight the potential of ddPCR as a valuable tool for monitoring minimal residual disease and disease progression in Hairy Cell Leukemia patients [7]. Solid tumors are often genetically diverse, with a range of mutations and variations. ddPCR assay can be utilized to identify these mutations with remarkable precision, aiding in the understanding of tumor heterogeneity and allowing for more personalized treatment strategies. For instance, mutations in genes like KRAS, EGFR, or BRAF can be detected, guiding the selection of targeted therapies [8].

A study by Alberto Verlicchi and group demonstrated that ctDNA analysis via ddPCR at key treatment stages, including pre- and post-chemotherapy, provides prognostic insights and improves the detection of recurrence, particularly when monitored longitudinally every three months post-therapy.This aspect of ddPCR is particularly relevant in the context of personalized medicine, where treatment decisions are based on specific genetic profiles [9].

Circulating Tumor cells (CTCs) is a minimally invasive alternative to traditional tissue biopsies allowing for real-time monitoring of tumor dynamics. Low abundance of CTCs in blood bloodstream leads to a low yield of DNA from the CTCs and hence requires techniques with higher sensitivity to detect the biomarkers. One of the studies has documented the detection of KRAS mutations in CTCs from blood samples of colorectal cancer (CRC) patients predicting those found in the tumor has become feasible due to the sensitivity of ddPCR [10].

Several studies have also demonstrated the utility of the ddPCR in detecting the Copy Number Variation (CNV) in the various types of cancers guiding clinical decisions. For example, Her2/neu Amplification detection in breast and gastric cancers in FFPE (Formalin fixed paraffin embedded tissue) extracted DNA. Higher accuracy in the detection of HER2/neu gene amplification in tumors having heterogeneity as well as low IHC scores and intermediate fluorescent signals reported by the Fluorescent In-situ Hybridization (FISH) technique can be effectively achieved through ddPCR technology. ddPCR has been applied to detect CNVs in melanoma, with a focus on genes like RREB1, CDKN2A, MYC, and MYB. The technology demonstrated high concordance with Chromosomal Microarray Analysis (CMA), a gold-standard technique for CNV detection [11].

Epigenetic biomarkers play a crucial role in the tumor pathology such as in tumor classification, understanding the resistance mechanisms and understanding the prognosis of the diseases. Multiple studies have demonstrated the utility of the ddPCR technology in detecting the Methylation biomarkers. A group of researchers evaluated the performance of novel epigenetic methylation biomarkers for detecting CRC using ddPCR, demonstrating high sensitivity and specificity in both tissue and plasma samples. It identified three key markers (C9orf50, KCNQ5, and CLIP4) that could detect early-stage CRC with over 70% sensitivity in plasma samples and 100% specificity in healthy controls [12].

A study by Paola Campomenosi and colleagues demonstrated the effectiveness of droplet digital PCR (ddPCR) in accurately detecting and quantifying miRNAs in lung cancer patients. Extracellular vesicles (EVs), particularly exosomes, are increasingly recognized as important biomarkers across various cancers. These nanoscale particles carry diverse biomolecules, including microRNAs (miRNAs), proteins, and lipids, which mirror the biological state of their cells of origin. The high sensitivity and precision of ddPCR make it an essential tool for analyzing EV-associated miRNAs, offering significant potential to enhance cancer diagnosis, prognosis, and treatment monitoring [13].

Studies have demonstrated that ddPCR can accurately monitor chimeric antigen receptor T- cell (CAR-T) kinetics, playing a crucial role in the monitoring and management of CAR-T cell therapies. ddPCR allows for the detection of CAR transgenes, enabling the quantification of CAR-T cell proliferation dynamics and helping clinicians assess the therapeutic response or early relapse [14].

ddPCR has also been used to study the tumor microbiome by quantifying the bacterial DNA in the tissue. It paves the way to identify potential biomarkers and gaining a deeper understanding of the role of bacteria associated with tumors [15].