An eye cancer cluster has affected nearly two dozen people and killed four within a 15-mile radius of a North Carolina town over the last decade - and experts have no idea what's causing it.

Ocular melanoma is a form of eye cancer that affects five in one million and is typically found in men in their 60s, but more than half of those diagnosed in Huntersville are women in their 30s or younger.

The most recent case was discovered five miles away in November when a 37-year-old woman was diagnosed with the eye tumor while eight months pregnant, leading to a complete removal of her eye.

Researchers have not been able to pinpoint exactly what's causing the cluster and Dr Brennan, the ophthalmologist leading the efforts, told Daily Mail Online: 'In all of our studies we’ve never found an environmental or genetic factor.’

SCROLL DOWN FOR VIDEO

Jessica Boesmiller, 37, who lives five miles outside of Huntersville, North Carolina, was diagnosed with ocular melanoma in November while eight months pregnant with twins

Summer Heath attended Hopewell High School and was diagnosed at 19, making her one of nearly two dozen people in the area affected by the eye cancer

The eye cancer has been found in people who work or live in a 15-mile radius of Huntersville, just north of Charlotte, North Carolina

A $100,000 grant was given to Dr Brennan in April to conduct a geospatial study on patients to find the commonality between them.

The study is examining 18 patients within a 15-mile radius, 13 of who are women and will follow their geographical history.

This came after tests done on the soil and water at Hopewell High School, where three of the patients attended, came up negative for any harmful toxins.

A genetic study later found that there were no hereditary causes for the disease.

Sue Colbert, the mother of one of the women who died, told Daily Mail Online that she is still looking for answers after tests failed to determine the cause of the cancer that killed her daughter Kenan when she was 28.

Mrs Colbert said she is hoping that the geospatial study will provide answers. 'I’m hopeful that Dr Brennan will be able to pinpoint some way that our lives interconnect and find some place in the environment that is a bull's-eye for this disease.'

She and her husband Kenny are still grappling with the loss of their daughter, who was one of the first diagnosed with ocular melanoma in the area in 2009.

‘We don’t believe this is coincidental. There are too many cases in our community of a rare cancer that was considered an ''orphan cancer'' when we first learned about it,' she said.

Ocular melanoma is a malignant tumor in the eye that can spread to other parts of the body and is especially dangerous if it reaches the liver. The disease is diagnosed in about 2,500 adults in the US each year.

WHAT IS OCULAR MELANOMA? Ocular melanoma is the most common primary cancer of the eye in adults. It is diagnosed in about 2,500 adults every year in the United States and occurs most often in lightly pigmented individuals with a median age of 55 years. OM is a malignant tumor that can grow and spread to other parts of the body - occurring in about 50 percent of patients. If the cancer spreads, there is a 15 percent survival rate and if it does not chances of survival are 80 percent. Although produced from the same cells in the body, called melanocytes, OM is different from skin melanoma and is not related to sun exposure. Ocular melanoma is the second most common type of melanoma after cutaneous and represents about five percent of all melanomas. Source: Ocular Melanoma Foundation Advertisement

The first cases of the disease that raised alarms came a decade ago when three women who had attended Hopewell High School in Huntersville were diagnosed in their 20s.

Kenan Koll was 23 when she began experiencing blurred vision and after new contacts and glasses could not fix her eyesight, a trip to the ophthalmologist diagnosed her with ocular melanoma in February 2009.

A year after having her eye removed, she learned that the cancer had spread to her liver, killing her by 2014.

Meredith Legg was two grades below Kenan at Hopewell High School and was also diagnosed in 2009.

Meredith, a basketball star at University of South Carolina, died in 2014 at the age of 26.

It wasn't until a third woman from the high school, 19-year-old Summer Heath, was diagnosed with ocular melanoma that panic began to swirl of a possible cancer cluster.

Of the studies conducted, the only commonality has been that the victims lived or worked within a 15-mile radius of Huntersville.

Nine of the first 12 patients that Dr Brennan studied were female and six younger than 30 years old.

This is especially unusual for a cancer that is found mostly in men over 60 with blue eyes.

While few of the patients have fit that criteria, two-thirds are young women, leading families and researchers to believe this is more than a coincidence.

'There is a substantial number of patients in a relatively small area that’s beyond the usual instance,' said Dr Brennan.

Kenan Koll, 28, (left) and Meredith Legg, 26, (right) both attended Hopewell High School in Huntersville, North Carolina, and were killed by ocular melanoma in 2014

The most recent case was found in Jessica Boesmiller, 37, who lives five miles outside of Huntersville in Cornelius, North Carolina.

Similar to Kenan, Jessica experienced blurred vision one night in November that lead to the diagnosis of ocular melanoma that was taking up half of her right eye.

Jessica was eight months pregnant with twins at the time and like nearly half of the other patients, had a complete removal of the eye.

She delivered healthy twins days before Christmas who were found to be cancer-free.

Dr Michael Brennan is leading the study to find what is causing the cancer cluster, however no environmental or genetic link has been pinpointed

As of yesterday, MRI and CT scans showed that her cancer has not metastasized.

Jessica said: 'The tumor pathology, however, is not what we would’ve preferred to hear- it was a class 2, prame positive, very large tumor. The stats of metastasis are highest with this class, though definitely not assured.'

Dr Brennan said Jessica will likely be involved in the new study focusing on a geospatial connection.

'We're taking dates and addresses of everyone - their every move, every church, home and any place they spent a lot of time,' said Brennan.

He added that this case has been discussed at international conferences in Australia raising the eyebrows of everyone in attendance.

'The medical community is surprised at the facts but we can't prove any environmental figures at this time,' he said.

While some patients are getting fatigued and have opted out of being involved in the study, Sue and Kenny Colbert said they are still fighting for their daughter.

'There’s a hole in my heart that will never heal and Kenan was so brave, such a fighter and she wanted to live so much that thinking about what she lost and her spirit keeps us going to look for answers,’ said Sue.