Testimony is set to begin in a U.S. federal lawsuit brought by four sisters who believe their breast cancer was caused by a drug their mother took during pregnancy in the 1950s.

The case, to be heard in Boston, involves a synthetic estrogen known as DES, prescribed to millions of pregnant women between the late 1930s and early 1970s to prevent miscarriages, premature births and other problems. Studies later showed the drug called “diethylstilbestrol” did not prevent miscarriages.

The Melnick sisters, who grew up in Pennsylvania, say they all developed breast cancer in their 40s.  Their mother took DES while pregnant with all four.  But they say their mother did not take DES while pregnant with a fifth sister, and that sister has not developed breast cancer. The Melnick sisters are among 51 women who have DES lawsuits pending in Boston against more than a dozen drug companies.  The Food and Drug Administration told doctors to stop prescribing DES to pregnant women in 1971 after a study found that the drug appeared to increase the risk of their daughters developing a rare vaginal cancer.  Thousands of lawsuits have been filed since then.  Many of those cases were settled.   DES was also widely prescribed in Canada.