So now they relied on a lack of light to increase melatonin levels, but did they have a control group who simply were fed/injected with melatonin? Because if there is a difference between that group, then it becomes even more interesting: what else does the body do in these circumstances of total darkness?
Of course, in general we need better sleep hygiene than what we do to ourselves now, and darkness at night would be one way. But for many it's not easy to just switch to a regime like that.
tamoxifen caused a dramatic regression of tumors in animals with either high nighttime levels of melatonin during complete darkness or those receiving melatonin supplementation during dim light at night exposure.
Of course, in general we need better sleep hygiene than what we do to ourselves now, and darkness at night would be one way. But for many it's not easy to just switch to a regime like that.