These are toxins that cause or sustain cancer. Some sources of these may be synthetic organic chemicals, certain inorganic chemicals, certain radioactive toxins such as Polonium 210 and certain electromagnetic toxins.

Polonium 210.
This is a radioactive element in the degradation chain of radium. It is active in very small amounts of a gram (thousandths of a microgram). 

Dr. Hulda R. Clark found that it changes the time schedule for the manufacture of DNA in the cell. The end result is the manufacture of more DNA than is needed for new growth and repair.

It is known that normal cells make DNA once every minute. DNA manufacture starts at exactly 00 seconds of each minute and stops at exactly 20 seconds of each minute.

Cells affected by polonium 210 have a delayed starting time and a longer DNA manufacture time. The more polonium 210 in the body the longer the DNA manufacture time will be and the more excess DNA will be made. Excess DNA causes nondifferentiated cells to grow causing malignancies.

This toxin is most often acquired from laundry bleach in drinking water. That means that any product containing chlorinated water may be contaminated.