HUNTERSVILLE, N.C. -- A mysterious eye cancer cluster near Huntersville just got bigger.

Ocular melanoma is a cancer so rare, it typically affects just five out of 1 million people a year.

But Monday night, experts revealed they have discovered several more cases in neighboring towns, bringing the number of patients to almost two dozen.

The focus of the cluster up until now had been on Huntersville.

“It was determined at that time to be Huntersville maybe Town hall or somewhere +15 miles,” Dr. Michael Brennan, an optometrist leading the investigation into the cluster, said at Monday’s town hall meeting.

“This is not just Huntersville,” he stressed.

He says experts are now expanding their focus to several other areas, including:

• Huntersville
• Denver
• Mooresville
• Davidson
• Mount Holly
• Belmont
• Concord

The investigation originally began looking toward Hopewell High school in Huntersville as ground zero.

Three patients attended school there. A dozen lived nearby.

Soil samples were collected from the school’s campus to see if there was a possible environmental cause for the cancer’s surge.

Currently, ocular melanoma does not have any known environmental or hereditary cause.

“For a number of under 30-year-olds to live in a tight geographic area I think that's unique and it deserves attention,” Dr. Brennan said.

Ocular melanoma is also extremely rare and usually affects males over 60, making this cluster of largely young female victims all the more unusual.

Now the investigation is looking to tackle a much larger area.

“I saw a lot of melanomas and every time I saw one I was afraid,” Brennan said.

Experts are now conducting tests, to find what, if anything, all these patients have in common.

“Is there some common intersection, did everyone play golf at the same golf course, did everyone run on the same trail?”

And the clock is ticking, at least four of the known local patients have died.

Families of the victims and the community members say they’re desperate for answers.

As of Monday, the cause of the growing cluster remains a mystery. Dr. Brennan estimated they should have some semblance of a concrete report by the end of 2017.