Make the first sentence usable
Lead with the reason for writing so the recipient does not have to decode a long emotional introduction. For a message about how to support someone during chemotherapy, use this factual base: acknowledge the diagnosis or treatment only as they described it and remember the practical burden around it.
Reduce the work of responding
Offer simple options, a narrow question, or a clear update that can be understood without another conversation. Offer one specific task, flexible company, or ordinary contact that they can accept or ignore. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Respect the boundary already visible
Do not prescribe cures, compare outcomes, ask for optimism, or share their health information. Leave medical decisions to clinicians and contact urgent or emergency services when there is immediate danger. A block, explicit refusal, legal restriction, or safety plan takes priority over the desire to explain more.