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Abstract: Cancer is a deadly disease taking the lives of about 14 million people annually. Most of the death caused by cancer is due to cancer metastasis. A lot is known and studied about the Metastatic properties of cancer, but there is a less explored region in the field of Cancer metastasis called Oligometastasis. This article talks about Oligometastasis, its mechanisms and relevance in clinical settings.
An operational definition of the oligometastatic state is when metastases are limited in number and location and are amenable to regional treatment. It can be regarded as an intermediate state between a localized and systemically metastasized disease. The term “Oligometastases” was coined in 1995 by Hellman and Weichselbaum, who used the term to identify a subset of patients who have disseminated cancer with few metastases (1).
For a few years, Oligometastatic disease has been in the spotlight, with a markedly growing number of new scientific papers every year and even penetrating the latest staging system of the American Joint Committee on Cancer (AJCC) for non-small cell lung cancer. It is not surprising as multiple studies have revealed a survival benefit in patients having Oligometastatic disease (OMD) compared to having Systemic metastases. In addition, it has been shown that local ablation of limited metastases can lead to prolonged disease control and eventually cure, such as in some oligometastatic HPV-positive oropharyngeal cancer cases.
Not yet standardized but already adopted by numerous investigators, the current terminology restricts the use of “Oligometastasis” to newly diagnosed cases (synchronously with the primary tumour). At the same time, the term “Oligorecurrence” should be reserved for metachronous dissemination (> 3-6 months after the primary cancer diagnosis) or to a new manifestation in patients with a history of prior metastatic disease. Finally, for patients going through anticancer therapies, the term “Oligoprogression” is used if a few distant lesions grow in size, or the word “Oligopersistence” is used if disease control is achieved (2).
Since there is no concrete evidence, it has been hypothesized that Polymetastatic and Oligometastatic disease differ in the spectrum of biological aggressiveness. There is an entire spectrum in which metastasis occurs. Within that spectrum, it is believed that there is a place where metastasis is more “laid back” in terms of aggressiveness which is oligometastasis. Generally, harsh conditions of primary tumour cells lead to sloughing off of cancer cells in blood to become circulating tumour cells which house another organ causing metastasis. In the case of oligometastasis, it is believed that perhaps the condition in the primary tumour is not very harsh, and the cells that break off are not very aggressive. The second proposed mechanism which explains oligometastasis is that the few tumour cells survive circulation since they are less aggressive and thus are not able to metastasize. The third proposed mechanism is that the organs where circulating tumour cells land are not very hospitable. Thus, they cannot thrive as they will do in systemic metastasis.
Most of the diagnoses of oligometastatic disease is made by Imaging due to the absence of biomarkers (3). However, oligometastatis can be diagnosed during staging with Imaging. In recent years, more patients have been designated as oligometastatic, especially in cases of colorectal cancer (4).
The utilisation of local ablative therapy or metastasis-directed therapy is an emerging management paradigm in oligometastatic and oligoprogressive cancer. Recent evidence has demonstrated that stereotactic ablative radiotherapy (SABR) targeting all metastatic deposits is tolerable and can improve progression-free and overall survival (2) (3). Thus, it can be concluded that though less is known about the mechanisms of oligometastasis, It still provides an opportunity to deal with metastasis and provides a better survival rate in cancer patients.
References
Treasure, T. (2012). Oligometastatic cancer: an entity, a useful concept, or a therapeutic opportunity?. Journal Of The Royal Society Of Medicine, 105(6), 242-246. https://doi.org/10.1258/jrsm.2011.110279
Szturz, P., & Vermorken, J. (2021). Oligometastatic Cancer: Key Concepts and Research Opportunities for 2021 and beyond. Cancers, 13(11), 2518. https://doi.org/10.3390/cancers13112518
Zayed, S., Correa, R., & Palma, D. (2020). Radiation in the Treatment of Oligometastatic and Oligoprogressive Disease. The Cancer Journal, 26(2), 156-165. https://doi.org/10.1097/ppo.0000000000000436
Lecture by Diane Reyes titled Theory of Oligometastasis and How Treatment is Supported by Imaging. Coursera. (2022). Retrieved 1 March 2022, from https://www.coursera.org/learn/cancer/lecture/B6Cdq/theory-of-oligometastasis-and-how-treatment-is-supported-by-imaging.
About the Author
Author: Sanyami Jain
Bio: Sanyami is a recent graduate from Daulat Ram College, Delhi University majoring in botany along with Zoology and chemistry as minors. Her research interests lie in Cancer biology, Immunology and Metagenomics. She is fascinated by the molecular mechanisms of cancer cells and how the exact mechanisms can be used to treat cancer. Sanyami is exceptionally passionate about having a career as a researcher. She aims to pursue higher studies in the domain of cancer biology. She aspires to become a cancer biologist and someday have her own research laboratory.
Editor: Himanshi Yadav
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