Eighteen grams equates to around just one eighth to one quarter of a cup full, they say – or one medium button mushroom (Agaricus bisporus).
Several studies have previously linked mushroom intake with slashing cancer risk, including prostate and cervical cancers.
Overall, these findings provide important evidence for the protective effects of mushrooms against cancer,' said study author John Richie, a professor of public health sciences and pharmacology at Penn State Cancer Institute.
'Future studies are needed to better pinpoint the mechanisms involved and specific cancers that may be impacted.'
Professor Richie said it's important to note that 18 grams is a 'very rough estimate' – although the data suggests the more mushrooms we eat, the lower the risk of cancer.
'The available methods used to estimate mushroom content in a person's diet is subject to a great deal of variability,' he told MailOnline.
'Also, the levels can vary greatly depending on the type of mushroom and whether and how they are cooked.'
Mushrooms are known as a good source of protein, vitamins, minerals, fibre and antioxidants.
They have a long history of being used in Asian medicines but their potential health benefits have only emerged in recent decades.
There have been an increasing number of studies suggesting that they could help anti-inflammation and antioxidation.
Of particular interest has been ergothioneine – a unique antioxidant and anti-inflammatory in mushrooms that humans are unable to synthesise on their own.