Solid tumors
Solid tumors are abnormal masses of tissue that develop when cells grow uncontrollably and do not contain cysts or liquid areas (NIH, national cancer institute). Solid tumors can be benign or malignant:
- Benign tumors are non-cancerous, do not invade nearby tissues, and do not spread to other parts of the body.
- Malignant tumors are cancerous, meaning they can invade surrounding tissues and spread to distant organs.
Solid tumors are grouped into several types:
- Carcinomas
Carcinomas are a prevalent type of solid tumor originating from epithelial cells, spreading through the lymphatic system. As they are mainly induced by endogenous (metabolically caused) or exogenous (smoke, radiation) DNA damage, they are more common in older patients and include cancers such as breast, lung, colon, and prostate cancer. - Sarcomas
Sarcomas are rather rare malignant tumors originating from mesenchymal tissues such as bones, muscles, and fat. They are categorized into soft tissue sarcomas (STS) and bone sarcomas, with STS being more common. These tumors are challenging to manage due to their rarity and diverse clinical presentations. - Lymphomas
Lymphomas are cancers of the lymphatic system, which is part of the immune system. While lymphomas can form solid tumors in lymph nodes and other tissues, they are distinct from other solid tumors due to their origin in immune cells.
Note: Unlike solid tumors, leukemias (cancers of the blood) mostly do not form tumor masses and are therefore considered separately.
Liquid biopsy in solid tumors
Monitoring and obtaining tissue samples from solid tumors present significant challenges due to their complex structure and genetic heterogeneity. Unlike leukemia and lymphoma, which can often be analyzed through blood samples, solid tumors typically require traditional tissue biopsies. These procedures are invasive, carry potential risks, and may only capture a limited snapshot of the tumor’s genetic landscape. Therefore, recent advancements in non-invasive techniques, such as liquid biopsies, offer promising alternatives for tumor analysis and monitoring.
Challenges with traditional biopsies
- Sampling Bias: Traditional biopsies often suffer from under-sampling bias, as they capture only a small portion of the tumor, which may not represent the entire (growing) tumor’s genetic diversity (1,2).
- Invasiveness: Tissue biopsies are invasive, painful, and not always feasible, especially for inaccessible tumors (3).
- Limited Monitoring: They provide a single-time snapshot and cannot be repeated frequently, limiting their utility in monitoring disease progression (2,4).
Liquid biopsy as an alternative
- Non-Invasive Monitoring: Liquid biopsies analyze circulating tumor DNA (ctDNA), circulating tumor cells, and other biomarkers in body fluids like blood, offering a non-invasive method to monitor tumors (5).
- Comprehensive Tumor Profiling: They can capture the genetic information of all tumor subclones, providing a more comprehensive view of tumor heterogeneity and evolution (6,7).
- Real-Time Disease Tracking: Liquid biopsies allow for continuous monitoring of disease progression and treatment response, helping to identify drug resistance mechanisms and minimal residual disease (2,4).
Applications and benefits
- Early Detection and Prognosis: Liquid biopsies can aid in the early detection of cancer and provide valuable prognostic insights by identifying mutations in key genes like TP53, which are frequently altered in solid tumors (8).
- Personalized Treatment: By analyzing the tumor’s genetic profile, liquid biopsies support tailored treatment decisions (7,9) helping to:
- identify patients who are responding well to therapy, ensuring continued effective treatment.
- detect patients who may no longer require treatment, reducing unnecessary interventions.
- optimize adjuvant or consolidation therapies by selecting the most effective treatment approach for each patient.
Conclusion
Liquid biopsies offer a promising, non-invasive alternative to traditional tissue biopsies for monitoring solid tumors. They provide a more comprehensive and dynamic view of tumor biology, enabling better disease management and personalized treatment approaches. As technology advances, liquid biopsies are likely to become integral to cancer care, overcoming the limitations of traditional biopsy methods.
MRD testing
LIQOMICS offers LymphoVista, a highly sensitive and specific ctDNA-based minimal residual disease (MRD) test, providing a powerful liquid biopsy solution for lymphomas. Our MRD tests for other cancers enable precise, non-invasive disease tracking. Learn more about our services here, and get in touch to explore how we can support your needs.
Literature
- Litchfield, D. K. et al. Representative Sequencing: Unbiased Sampling of Solid Tumor Tissue. SSRN Electron. J. (2019) doi:10.2139/ssrn.3404257.
- Siravegna, G., Marsoni, S., Siena, S. & Bardelli, A. Integrating liquid biopsies into the management of cancer. Nat. Rev. Clin. Oncol. 14, 531–548 (2017).
- Marrugo-Ramírez, J., Mir, M. & Samitier, J. Blood-Based Cancer Biomarkers in Liquid Biopsy: A Promising Non-Invasive Alternative to Tissue Biopsy. Int. J. Mol. Sci. 19, 2877 (2018).
- Le Rhun, E., Seoane, J., Salzet, M., Soffietti, R. & Weller, M. Liquid biopsies for diagnosing and monitoring primary tumors of the central nervous system. Cancer Lett. 480, 24–28 (2020).
- Marrugo-Ramírez, J., Mir, M. & Samitier, J. Blood-Based Cancer Biomarkers in Liquid Biopsy: A Promising Non-Invasive Alternative to Tissue Biopsy. Int. J. Mol. Sci. 19, 2877 (2018).
- Pinzani, P. et al. Updates on liquid biopsy: current trends and future perspectives for clinical application in solid tumors. Clin. Chem. Lab. Med. CCLM 59, 1181–1200 (2021).
- Balaji, S. A. et al. Analysis of solid tumor mutation profiles in liquid biopsy. Cancer Med. 7, 5439–5447 (2018).
- Garrido-Navas, M. C. et al. The Polemic Diagnostic Role of TP53 Mutations in Liquid Biopsies from Breast, Colon and Lung Cancers. Cancers 12, 3343 (2020).
- Moding, E. J., Nabet, B. Y., Alizadeh, A. A. & Diehn, M. Detecting Liquid Remnants of Solid Tumors: Circulating Tumor DNA Minimal Residual Disease. Cancer Discov. 11, 2968–2986 (2021).
Author: Dr. rer. nat. Lisa Baum, Bioinformatician and Data Scientist, LIQOMICS
