There have been many studies about the anti-cancer effects of spirulina. These are mostly cell-based studies because it is very difficult to perform clinical trials for cancer.
One such study concluded that the tetrapyrrolic components in spirulina substantially decreased the proliferation of pancreatic cancer (1). Another study showed that spirulina slowed the growth of and even killed some types of tumors in mice (2). Yet another study concluded that some components in spirulina can be considered as agents with anti-cancer properties that may be used for colon cancer prevention and treatment (3).
With so many references available, it seems clear that including spirulina as part of a balanced and healthy diet is a good way to reduce the risks of cancer.
1. Renata Koníčková, Kateřina Vaňková, Jana Vaníková, Katerina Vánová, Lucie Muchová, Iva Subhanová, Marie Zadinová, Jaroslav Zelenka, Ales Dvořák, Michal Kolář, Hynek Strnad, Silvie Rimpelová, Tomas Ruml, Ronald J. Wong, Libor Vítek, Anti-cancer effects of blue-green alga Spirulina platensis, a natural source of bilirubin-like tetrapyrrolic compounds, Annals of Hepatology, Volume 13, Issue 2, 2014, Pages 273-283, ISSN 1665-2681.
2. Akao Y, Ebihara T, Masuda H, Saeki Y, Akazawa T, Hazeki K, Hazeki O, Matsumoto M, Seya T. Enhancement of antitumor natural killer cell activation by orally administered Spirulina extract in mice. Cancer Sci. 2009 Aug;100(8):1494-501. doi: 10.1111/j.1349-7006.2009.01188.x. Epub 2009 May 6. PMID: 19432881.
3. Śmieszek A, Giezek E, Chrapiec M, Murat M, Mucha A, Michalak I, Marycz K. The Influence of Spirulina platensis Filtrates on Caco-2 Proliferative Activity and Expression of Apoptosis-Related microRNAs and mRNA. Mar Drugs. 2017 Mar 7;15(3):65. doi: 10.3390/md15030065. PMID: 28272349; PMCID: PMC5367022.
Other interesting links: