BOSTON – At first, the Melnick sisters thought it was just a cruel coincidence that two of them were diagnosed with breast cancer.

But when two more sisters were given the same diagnosis, they came to suspect that a drug their mother took in the 1950s while she was pregnant had something to do with it.

The four sisters are now suing a former maker of DES, or diethylstilbestrol, in a case set to unfold in federal court today, when it will become one of the first of scores of such claims around the U.S. to go to trial. The Melnick women are seeking unspecified damages.