A 2015 study concluded that regular shiitake consumption resulted in improved immunity and anti-inflammatory processes.
Another report demonstrated that Brazilian aqueous extracts of shiitake displayed inhibitory activity against the growth of human laryngeal and cervical cancer tumor cell lines.
X. Dai et al. Consuming Lentinula edodes (shiitake) mushrooms daily improves human immunity: A randomized dietary intervention in healthy young adults. Journal of the American College of Nutrition, 34 (6). 478-487. (2015)
T.C. Finimundya et al. Aqueous extracts of Lentinula edodes and Pleurotus sajor-caju exhibit high antioxidant capability and promising in vitro antitumor activity, Nutrition Research. 33 (1), 76-84. (2013)