Cancer is still a significant global health concern. Enormous efforts have been made in cancer research in the past and present, and significant advancements in diagnosis and therapy have been achieved. In order to significantly enhance life quality and prolong the lifespan of cancer patients, various challenges still need to be overcome. The biggest challenge is coming up with efficient treatment options. Numerous medicines had been beneficial in these cancer models but had decided to be eliminated in clinical trials due to either inefficiency or intolerable side effects as a result of conventional cancer models’ inadequate recapitulation of human tumors1.
Traditional two-dimensional (2D) cell line cultures and patient-derived tumor xenografts (PDTXs) have been employed as tumor models for a long time and have had a significant impact on cancer research2. However, comprehensive research into the genetics, pathophysiology, and etiology of cancer has been conducted. It has been discovered that the outcomes from cell lines and patient-derived tumor xenografts (PDTXs) do not always correspond to the actual clinical situation1,2.
Three-dimensional (3D) organoid technology has emerged as a new research model, achieved major advancements and caught on the attention of researchers in recent years2,3. Searching by Simian et al. in PubMed, the number of publications using the keyword “organoids” has increased incredibly since 2011, which demonstrates the dynamic expansion of research on organoid models2. Organoids are minuscule replicas of in-vivo tissues and organs that accurately mimic the structures and unique activities of a particular organ. These three-dimensional (3D) constructions offer a promising, nearly physiological representation of human malignancies and greatly help a wide range of future cancer research applications. Organoids have significant advantages over conventional models and have been used in the study of cancer, genetic disorders, infectious diseases, and regenerative medicine1,2,3. The pros and cons of using organoids as compared with other cancer modelings were reviewed in this writing1.

Historical Background
American biologist and anatomist Ross G. Harrison, who succeeded in growing nerve cells in lymph acquired from a frog in 1907, contributed the “cell culture” experimental method to science that would host many studies in the advancing years1,4.
This experimental approach is the origin of tissue culture technology, from which cell lines became miraculous to the improvement of medicine. According to this improvement, traditional two-dimensional (2D) cell lines provide beneficial properties. For instance, they are affordable, simple to maintain and grow, and the technology is not too complicated1,3. High-throughput drug screening can use cell lines, and different cell line populations with histological and genetic alterations can simulate various clinical scenarios and medicine reactions1. Gene editing is also possible with cell lines. Significant advancements have been made in the in vitro (IV) identification of molecular and carcinogenic targets through improved gene editing. Due to their indispensable significance in the study of disease development and medication screening, cell lines have become the most popular research model in recent years1.
But there are a few flaws with the two-dimensional (2D) cell line model. For instance, they require significant adaptation and selection to in vitro 2D culture conditions and are produced inefficiently from primary patient material. The generated cell lines may have undergone significant genetic modifications and no longer recapitulate the genetic heterogeneity of the original tumors because only uncommon clones can expand and be maintained through numerous passages1,3.
Second, there is only two-dimensional (2D) growth in the cell line model; there are neither distal external signals from the circulatory system nor external signals from neighboring cells. As a result, this model is unable to incorporate essential systems and microenvironments that typically exist under particular physiological or pathological circumstances1,2,5. These limitations alter the behavior and molecular properties of cancer cells, altering their susceptibility to chemotherapy, as well as their potential to spread in vivo. Traditional cell line disease models frequently misconjecture the disease development and treatment response in vivo due to these major drawbacks, which severely restricts the use of cell line models in experimental research1.
Cancer research has greatly benefited from using 2D cell line cultures as well as patient-derived tumor xenografts (PDTXs) tumor models3. PDTXs have the virtue of significantly better imitating the biological properties of the human tumor than 2D culture models. PDTXs are formed by transplanting recently obtained patient material into humanized or immunodeficient mice1,2,3. In addition to being able to engage and communicate with the host matrix and immune cells, PDTXs can also maintain the 3D structure of the tumors as well as their original genomic and phenotypic properties. As a result, they are more eligible for use in preclinical animal experiments, medicine response prediction, and evaluating the effectiveness of novel tactics3. PDTXs have significant predictive value and are necessary for result authentication in crucial clinical research, according to the aforementioned benefits. Preclinical testing of experimental cancer therapeutics is facilitated by the capacity to serially transplant tumor tissues into increasing numbers of animals3,6. The use of animals and the low engraftment efficiency for specific patient tumor subsets are drawbacks of PDTXs6. Additionally, the method is costly, time and resource-consuming, and PDTXs may evolve into tumors that are mouse-specific tumors1.
Scientists are always trying to develop a new research model that combines the benefits of cell lines and PDTXs due to the drawbacks of the limits of both cell lines and PDTXs. In 2009, Sato et al. published the first description of an organoid culture technique that enables intestinal stem cells (ISCs) to develop in vitro for a prolonged time in a 3D extracellular matrix (ECM), ushering in a new age2. Organoids have made significant advances in the study of disease mechanisms, drug screening, and precision medicine. They are widely used to understand stem cell biology, organogenesis, and human pathology1,3,6.
Organoids have many benefits because they are cheaper and more time-efficient, but they still have a high success rate1. Organoids capture the genetic and phenotypic variability of the original tissue by preserving the 3D structure of the original tissues. Organoids can serve as a platform for very effective and precise drug screening, directing clinical precision treatment and personalized treatment1,7. Organoids are eligible for gene modification. For instance, the CRISPR-Cas9 system and organoids together offer a novel way to investigate cancer gene mutation1,2,3,7. Organoids can be modified to create different models, work together to build a biological bank (biobank), and establish a thorough and precise experimental platform.

However, organoids still have drawbacks1,7. For instance, organoid culture requires more time and money than cell lines. The absence of stroma, blood arteries, and immune cells in organoid culture is one of its current flaws. Future research will focus on the potential for creating co-culture systems that include extracellular (and microbial) components. Another potential drawback is that advanced cancer organoids frequently develop more slowly than organoids formed from normal epithelium, which may cause organoids derived from contaminated normal epithelium to outgrow tumor organoids. This observation is most likely the result of tumor organoids having a considerably greater probability of mitotic failure and subsequent cell death. Future research will reveal more details about this.
Conclusion
2D cell lines, PDTXs, and organoids have pros and cons1. According to the target, requirements, and circumstances, the most eligible research model should be chosen for experimental studies.

This writing outlined recent findings and highlighted the benefits of existing organoids in tumors, demonstrating the limitless potential of organoids as a novel disease model. Organoids have also been successful in studying medication toxicity, neuropsychiatric disorders, and tissue formation1,3. Organoids still have drawbacks in vascularization, the immunological microenvironment, etc1,7. Despite the drawbacks of organoids, early genome, transcriptome, and biochemical examinations of human cancer organoids have led to the development of new and alternative approaches for classifying cancer patients that will respond to cytotoxic and targeted chemotherapies.If these discoveries are encouraged by well-conducted prospective clinical trials, organoid technology may figure a significant role in determining how future cancer patients will be treated2,3. And consequently, organoids will be utilized more frequently and directly in the clinical treatment of cancer patients and provide insight.

References:
- Huang, Y., Huang, Z., Tang, Z., Chen, Y., Huang, M., Liu, H., . . . Jia, B. (2021, November 16). Research progress, challenges, and breakthroughs of organoids as disease models. Retrieved October 29, 2022, from https://www.frontiersin.org/articles/10.3389/fcell.2021.740574/full
- Xu, H., Lyu, X., Yi, M., Zhao, W., Song, Y., & Wu, K. (2018, September 15). Organoid technology and applications in cancer research – journal of hematology & oncology. Retrieved October 29, 2022, from https://jhoonline.biomedcentral.com/articles/10.1186/s13045-018-0662-9#Sec2
- Drost, J., & Clevers, H. (2018, April 24). Organoids in cancer research. Retrieved October 30, 2022, from https://www.nature.com/articles/s41568-018-0007-6
- Söğüt, M. S. (2022, July 18). Organoidler: Organizmayı Üç Boyutlu Taklit Etmek. Retrieved October 30, 2022, from https://bilimgenc.tubitak.gov.tr/makale/organoidler-organizmayi-uc-boyutlu-taklit-etmek
- Clevers, H., & Tuveson, D. A. (2019,March). Organoid models for Cancer Research – annual reviews. Retrieved October 30, 2022, from https://www.annualreviews.org/doi/abs/10.1146/annurev-cancerbio-030518-055702
- Tuveson, D., & Clevers, H. (2019, June 7). Cancer modeling meets human organoid technology | science. Retrieved October 30, 2022, from https://www.science.org/doi/10.1126/science.aaw6985
- Huang, Y., Liu, K., Wang, Y., Yang, Y., Xiong, L., Zhang, Z., & Wen, Y. (2021, January 1). Application and research progress of organoids in cholangiocarcinoma and gallbladder carcinoma. Retrieved October 30, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7840717/
Figure References:
- Xu, H., Lyu, X., Yi, M., Zhao, W., Song, Y., & Wu, K. (2018, September 15). Organoid technology and applications in cancer research – journal of hematology & oncology. Retrieved October 29, 2022, from https://jhoonline.biomedcentral.com/articles/10.1186/s13045-018-0662-9#Sec2
- Huang, Y., Huang, Z., Tang, Z., Chen, Y., Huang, M., Liu, H., . . . Jia, B. (0001, January 01). Research progress, challenges, and breakthroughs of organoids as disease models. Retrieved October 29, 2022, from https://www.frontiersin.org/articles/10.3389/fcell.2021.740574/full
- Tuveson, D., & Clevers, H. (2019, June 7). Cancer modeling meets human organoid technology | science. Retrieved October 30, 2022, from https://www.science.org/doi/10.1126/science.aaw6985
Inspector: Ahmet Alperen CANBOLAT