Solidarity is a fundamental social value in many European countries, though its precise practical and theoretical meaning is disputed. In a health care context, I agree with European writers who take solidarity normatively to mean roughly equal access to effective health care for all. That is, solidarity includes a sense of justice. Given that, I will argue that precision medicine represents a potential weakening of solidarity, albeit not a unique weakening. Precision medicine includes 150 targeted cancer therapies (mostly for metastatic (...) cancer), all of which are extraordinarily expensive. Our critical question: Must a commitment to solidarity as defined mean that all these targeted cancer therapies should be guaranteed to all within each country in the European Union, no matter the cost, no matter the degree of effectiveness? Such a commitment would imply that cancer was ethically special, rightfully commandeering unlimited resources. That in itself would undermine solidarity. I offer multiple examples of how current and future dissemination of these targeted cancer drugs threaten a commitment to solidarity. An alternative is to fund more cancer prevention efforts. However, that too proves a threat to solidarity. Solidarity, with or without a sense of justice, is too abstract a notion to address these challenges. Further, we need to accept that we can only hope to achieve “rough justice” and “supple solidarity.” The precise practical meaning of these notions needs to be worked out through a fair and inclusive process of rational democratic deliberation, which is the real and practical foundation of just solidarity. (shrink)