A Massachusetts firm won Food and Drug Administration permission Wednesday to advertise that it has developed the first improved Pap smear in 50 years.

The ThinPrep test by Cytyc Corp. is a new way to prepare Pap smears so that this vital test for cervical cancer isn’t marred by a smudged laboratory slide.

Pap smears can detect abnormal cells before they become cancerous, or find cancer early enough to cure it. Cells are scraped from the cervix, smeared onto a microscope slide and analyzed for abnormalities.

Sometimes excess blood or mucus mingled with the cells smudge the Pap slide, however, and women must be retested.

With ThinPrep, doctors don’t prepare the slide. Instead, they stick the cervical swab into a special vial where chemicals separate the cells from the trash. The laboratory filters the cells onto a slide for a cleaner test.