Employing a dynamic systems approach, this chapter investigates the use of one particular metaphor – the “cancer card”– on an online forum dedicated to cancer. Far from being a common Card Game metaphor with a stable source–target mapping, the metaphor is collaboratively developed (i.e. used, re-used, adapted) to express the idea that patients can use their illness to their advantage in a variety of situations, while also reflecting a broader tendency to employ humor as a strategy for coping with adversity. An analysis of all 106 instances of “(cancer) card(s)” on one of the threads of the forum shows that, though related to English expressions like “play the […] card” and to conventional conceptual metaphors like LIFE IS A GAME, its use is specific to the interactions among the members of this online community. Our analysis of the “cancer card” as a group-specific “metaphoreme” (Cameron & Deignan 2006) emphasizes that multiple interacting factors must be considered to account for such rich and complex phenomena as the use of metaphors in online interactions.