En lo que

Since the expression en lo que is composed of common words, it might slip by your notice at first. It is one way convey while + activity.

• En lo que me bañaba, llegó la señora de la renta a buscarme. I was showering when the landlady came by looking for.
• En lo que me visto. While I'm getting dressed. In the time it takes me to get dressed.

Mientras could work here as well.

En lo que va de

With ir de, this is a common way to express so far + period of time.

• 300 homicidios en lo que va del año. 300 homicides so far this year. You see this a lot in the official reporting of year-to-date statistics.
• En la que va del mes. Counting from the beginning of the month until now. So far this month.

If the period in question is unimportant or obvious from the context, you can just say hasta la fecha: Hasta la fecha no me ha dicho nada. He hasn't said anything to me so far.