Episode 20

"Cancer Cell II (Part I)" (がん細胞II（前編)) is the twentieth episode of the Cells at Work! anime.

Synopsis
Cancer Cell reappears, and harmful bacteria wreak havoc on the intestinal environment. With the body in unprecedented danger, White Blood Cell and his comrades fight to protect the future.

Plot
Part 1: Normal Cell, AE3083, and the platelets continue to evacuate. Memory T Cell remembers Cancer Cell's techniques, giving his team the advantage, but they are shocked when Regulatory T Cell defends Cancer Cell, believing he is a Normal Cell that needs to be protected. U-1146 is injured and Cancer Cell traps him in a pod, saying he's fascinated with him for the contradiction of being a defender when his function is to kill. Cancer Cell strengthens himself by absorbing the carcinogens in the toxic gas and plans to kill the body so that everyone will be equal in death. Despite hearing this, Regulatory T Cell continues to defend him and effortlessly beats up NK Cell and Memory T Cell. Normal Cell is cornered by harmful bacteria. The lactic acid bacterium tries to defend him, but is swatted aside. Normal Cell orders it to run and it does. The bacteria start torturing him.

Returning characters

 * Cancer Cell
 * Natural Killer Cell
 * U-1146
 * Killer T Cell
 * Regulatory T Cell
 * Normal Cell
 * Lactic Acid Bacteria
 * Goblet Cell
 * Intestinal epithelial cells
 * AE3803
 * Platelet Division