Morphine-like opioids can slow down or speed up the growth of malignant tumors by affecting growth factor receptors. Which one they do, depends on the type of cancer. Lung cancer seems to be slowed down by morphine: https://journals.lww.com/anesthesia-analgesia/subjects/Preclinical Pharmacology/Fulltext/2016/12000/Morphine_Suppresses_Lung_Cancer_Cell_Proliferation.14.aspx .
morphine aint only slowing down cancer in the lung but also your damn breathing. interesting mechanism, less breathing less likely for cancer to grow hmm