With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: There have not always been "many therapies offered outside of conventional cancer treatment centers and based on theories found in biomedicine. These alternative cancer cures have often been described as 'unproven,' suggesting that appropriate clinical trials have not been conducted and that the therapeutic value of the treatment is unknown." However, "many alternative cancer treatments have been investigated in good-quality clinical trials, and they have been shown to be ineffective...The label 'unproven' is inappropriate for such therapies; it is time to assert that many alternative cancer therapies have been 'disproven'."
text_B: Have there always been many therapies offered outside of conventional cancer treatment centers and based on theories not found in biomedicine?
NO.