Complex sentence: Now, however, very sensitive molecular biology tests are available--based on DNA, RNA or proteins--and these can measure minute levels of cancer cells in tissue samples, sometimes as low as one cancer cell in a million normal cells.
Split into simpler sentences: Now, however, very sensitive molecular biology tests are available, based on DNA, RNA or proteins. These can measure minute levels of cancer cells in tissue samples, sometimes as low as one cancer cell in a million normal cells.