Visceral Cankers were originally added as a secondary objective during the The Hallowed Blight Event in 2018 that Survivors had to harvest in order to fill vials with Putrid Serum.
The Hallowed Blight
The The Hallowed Blight would spawn 2 Visceral Cankers in the Trial Grounds by default, which could be increased by using then iteration of the Pustula Petals Offering.
Harvesting the Visceral Canker would yield bonus Bloodpoints, as well as slowly fill a vial at the top right of the screen, with a full vial being converted into a Putrid Serum , a temporary currency for the in-game Store .
After harvesting a Visceral Canker, it would dry out and could no longer be interacted with.
When selecting an incomplete "Bountiful Harvest" Challenge in Tome V - Unleashed, the procedural Map generator will spawn a Visceral Canker somewhere on the Trial Grounds.
In order to complete the Challenge that Survivor must harvest it.
Only the Survivor having selected the Challenge can interact with the Visceral Canker.