The only relation I know to SASS is that you can take advantage of SASS’ nesting. For example:

.list {

  &__header { /* stuff */ }

  &__item { /* stuff */ }

  &--modifier { /* stuff */ }

  &--modifier2 { /* stuff */ }

}

Reference: http://alwaystwisted.com/post.php?s=2014-02-27-even-easier-bem-ing-with-sass-33