The wider availability of genomic sequencing, notably gene panels, in cancer care allows for personalised medicine or the tailoring of clinical management to the genetic characteristics of tumours. While the primary aim of mainstream genomic sequencing of cancer patients is therapy-focussed, genomic testing may yield three types of results beyond the answer to the clinical question: suspected germline mutations, variants of uncertain significance (VUS), and unsolicited findings pertaining to other conditions. Ideally, patients should be prepared beforehand for the clinical and psychosocial consequences of such findings, for themselves and for their family members, and be given the opportunity to autonomously decide whether or not to receive such unsolicited genomic information. When genomic tests are mainstreamed into cancer care, so should accompanying informed consent practices. This paper outlines what mainstream oncologists may learn from the ethical tradition of informed consent for genomic sequencing, as developed within clinical genetics. It argues that mainstream informed consent practices should focus on preparing patients for three types of unsolicited outcomes, briefly and effectively. Also, it argues that when the chance of unsolicited findings is very low, opt-out options need not be actively offered. The use of a layered approach - integrated in information systems - should render informed consent feasible for non-geneticist clinicians in mainstream settings. (Inter) national guidelines for mainstreaming informed consent for genomic sequencing must be developed.