Here is a brief and basic summary of the concept of why we're concerned not only about the cancer we can see but the potential cancer we can't.
I've mentioned in posts in the past about the settings in which local therapy might be appropriate for someone even when we know the cancer is advanced/metastatic. Here's a brief video that discusses some of these issues, including a situation in which the local treatment isn't specifically aimed at addressing a symptom, as is the usual reason for treating with local therapy for metastatic cancer, but is rather what I'd consider the "Get the Lead Runner" strategy:
I'm interested in your thoughts.
Why is Chemotherapy a Recommended Part of the Treatment Plan for Most Patients with Lung Cancer, even Early Stage?
Here's a brief video just discussing the rationale for why a systemic treatment like chemotherapy is recommended not only as the cornerstone of treatment for advanced lung cancers, which makes intuitive sense, but also for the majority of patients with earlier stages of lung cancer as well.
I hope it's helpful.