How does stress effect or weaken the immune system, especially in a cancer recovery patient?

Complicated: The pop notion that "stress weakens the immune system" is simplistic. Selye actually distinguished good (motivates you) and bad (you're helpless) stress; don't expect this to be decisive in your long-term prognosis. Your oncologist can guide you in managing the difficulties of daily living. Don't trouble yourself over the huge amounts of speculative material from cell culture labs, ; good luck.

Very complex things: There's a big difference between acute ; chronic stress. The hypothalamic-pituitary axis has vital responses to ensure survival in acute stress -- and these responses are very connected to immune responses. Cortisol, epinephrine, and ne pour out, stimulating lymph nodes ; spleen; interleukins stimulate immune cells to secrete cytokines. In a chronic stress feedback loop, these can be suppressed.