Final answer:
The best course of action would be to remove the cancerous lesion and inform the patient, considering the need for patient consent and the potential need for a more extensive resection. Consultation with a senior surgeon may also be appropriate for guidance.
Step-by-step explanation:
The correct action in this scenario, where a cancerous lesion is discovered during a polypectomy, would be option C: Remove the cancerous lesion and inform the patient. Performing the additional procedure may be necessary to remove cancerous tissue and potentially cure the patient, given the early detection. However, this typically would occur after obtaining informed consent from the patient, which is a crucial step not explicitly mentioned in the options provided. Therefore, while removing the lesion is the right clinical step, it is also essential to ensure proper communication and informed consent. If this situation arises intraoperatively, and consent for a more extensive procedure has not been attained previously, it might be appropriate to close and then discuss the situation with the patient afterwards, seeking their consent for a new, more extensive procedure.
In any case, consulting with a senior surgeon, as suggested by option D, may also be prudent depending on the severity and nature of the lesion, as well as the original operation plan and what the surgeon feels comfortable with considering their level of expertise. Direct and thorough communication with the patient post-operatively is crucial to discuss the findings, the implications, and future treatment options. This step should not be overlooked or replaced with discussion with the patient's family unless the patient has designated them as their decision-maker.