Surgical residue, which is well understood, means that the scalpel did not eliminate all the cancer cells. Individual cancer cells are very small, about 10-20 microns in diameter. 10 microns is equal to one hundredth of a millimeter, that is, it takes 100 cancer cells in a straight line to be as long as 1 millimeter, which is as thin as a hair. These individual cancer cells are too small to be seen by the naked eye and touched by the hand, and cannot be detected even by CT, MRI and other imaging examinations. Cancer cells are not arranged one by one in a straight line, but gather into a group and grow like a sphere, and when their number and size increase, they form a lump, called a cancerous tumor or cancer mass. A cancer mass of 1 mm in diameter contains about 1 million cancer cells, but the highest level of ultrasound, CT or MRI in hospitals cannot detect it at present. A cancerous mass of 1 cm in diameter contains about 1 billion cancer cells, which can be felt by hand and scanned by color ultrasound if it grows in the superficial part of the breast; CT can scan it if it grows in the lung; and gastroscopy can directly see it if it is in the stomach. The surgeon can take out all the visible and palpable cancer masses, but a few cancer cells around the masses remain, which lays the foundation for recurrence after surgery. The English name for cancer is cancer, which also stands for “Cancer” and is derived from the Latin word for crab. The association of cancer with crab is a visualization of the way the cancer mass grows like a crab. The cancer mass often grows out in the surrounding area in tiny “crab-like” pieces, which is the medical term for “invasion (infiltration)” into the surrounding tissue. This unique growth pattern can easily lead to surgical removal of the surrounding – invisible and invisible cancer cells.