Detect Evil will detect the [evil] aura of the active Necrotic Cyst (and Tumor) spells on the victims.

Detect Undead will detect the cysts themselves, as they are undead...things.

Detect Magic will detect the active spells, as well as identify them as Necromancy school.

Spellcraft will allow somebody witnessing a victim operate under the effect of Necrotic Tumor identify the spell in place.