Does cancer chemotherapy weaken the aura defenses against spirit attachments?

This is very much the case and is quite unfortunate. It is one of the many ironies that being attacked from within by one's own cells that have undergone a malignant transformation, to grow wildly and intrude on normal tissue and cause self-harm in the process, calls forth the best medicine can do, in the form of ingesting poisons to kill living cells that are rapidly dividing, which also undermines the immune system and makes the person more vulnerable to invading viruses which are responsible for cancer 85% of the time. There are also effects on the aura, and that energetic shield normally prevents dark spirits from gaining a foothold where they can do serious damage to a person. This is true for many kinds of heavy medication that suppress bodily functions like anesthesia and opioid drugs. It is also the case that, like antipsychotic medication, the chemotherapy agents attract many negative thought forms corresponding to fears of cancer that people generate quite frequently, and that is an extra penalty of using heavy medication, that patients will ingest symptoms of the illness their medication is designed to treat, so there is a conflict underway energetically, always, where the treatment can become as bad as the illness underway, in some respects, and result in a worsening of things overall. So chemotherapy is a mixed blessing, indeed, and far from the best answer except in the absence of divine healing.