In her mind’s eye, Pamela Thompson summits California’s 14,000-foot Mount Shasta on a beautiful day.

“It’s absolutely clear. Blue sky. You can see forever,” Thompson said. “I really want to make it.”

This month Thompson will climb Shasta — the second-highest peak in the Cascade Range — to raise funds and awareness for breast cancer prevention.

Thompson, manager of adult education at the Arnold Arboretum, has raised nearly $8,000 for the nonprofit Breast Cancer Fund, whose prevention focus is on reducing toxins in our everyday environment. She’ll be taking part in the fund’s Climb Against the Odds from June 16 to June 21.

Thompson, 51, was diagnosed with breast cancer in 2010. The call confirming her lump was cancerous came while she was at her dying father’s bedside.

“I took the call in the bathroom at the nursing home,” Thompson recalls. “I fell out of the bathroom … and fell into the arms of my family.”

Thompson credits her 18-year-old daughter, Ailsa Jeffries, an incoming Harvard freshman, for taking a practical approach that helped her during those first difficult days.

“As a family, we approached it as a problem that can be solved,” Thompson said. “It does turn your world upside down.”

She underwent a year of treatment, including a single mastectomy for ductile carcinoma in situ — cancer in a milk duct that hasn’t spread — followed by reconstructive surgery.

Thompson became interested in the climb when she came across one of the Breast Cancer Fund’s newsletters, and then applied.

Never an avid exerciser or distance hiker, Thompson had just last fall started riding her bike to the Arboretum from her home in Milton. On hearing, in January, that she’d been accepted on the climb, she threw herself into training. She began walking and then running short distances, gradually lengthening to four or five miles. She also began hiking in the Blue Hills, first without a pack and then hauling up to 30 pounds. She has lost 10 pounds and today is running farther than she ever thought she would.

In April, her preparations took a serious hit when she sprained her ankle during her first hike on Great Blue Hill. That forced her to take two weeks off of training. When she restarted, she built intensity slowly.

Even early this month, the ankle still felt a bit dodgy, Thompson admitted — but better when she’s hiking. She has no intention of letting it interfere with the Shasta climb.

“I’ve gotten this far, I’m not turning back,” Thompson said.

Susanne Pfeiffer, Thompson’s sometime hiking partner and a horticultural technician at the Arboretum, said she has no doubt her friend will make it. After a long day of work, sometimes followed by a public event, Thompson and Pfeiffer will grab their gear and head to the Blue Hills for a hike.

“Pam … has this burst of energy, a fire inside her. She just keeps going and going,” said Pfeiffer, who credited Thompson with inspiring her to get out hiking more often. “She’s up for the challenge. Pam’s a fighter. She’ll make it to the top and make friends along the way, because that’s how she is.”

As Thompson’s departure approaches, mountaineering gear sent east by the San Francisco-based Breast Cancer Fund has been piling up in her living room: water bottles, a pack, specialized underlayers, trekking poles, and a warm down coat and shell. Thompson figures she’s pretty well equipped, except for food and a sleeping pad.

Mount Shasta, a dormant volcano, is the fifth-highest peak in California. With warm weather below, part of the climb will be done in snow, by roped teams equipped with crampons and ice axes.

The Breast Cancer Fund is working to prevent breast cancer by reducing toxins in household items such as food cans, cosmetics, cleaning products, and toys. Thompson said that with breast cancer rates for women 50 and older tripling in just a generation and just 5 percent to 10 percent of breast cancer patients having previous cancer in their family or known breast cancer genes, it seems that environment is an issue.

“We’re not getting it from our mothers and grandmothers,” she said. “I’m the first one in my family. … I really would like answers. I’d like my daughter to know more.”

Thompson flies out of Boston for California on June 14. She’ll spend the next day in “snow school,” learning crampon technique, how to hike roped in with other climbers, and how to use an ice ax, including the finer points of self-arrest should she start sliding.

The next day, Thompson will meet with the group’s guides and the rest of the team. On Monday she’ll be briefed and go though gear checks.

The climb starts Tuesday at a trailhead at 6,900 feet and proceeds up to a base camp at 9,600 feet. The plan calls for an early bedtime after dinner. On Wednesday, the group will rise at 1 a.m. for the 12- to 16-hour round trip to the summit, hiking up roped together in teams of five. They’ll spend that night back at the base camp before hiking out the next day.

Thompson has imagined the hike, seeing footprints in the snow ahead as she and her roped-in partners trek relentlessly uphill.

“I’ve seen myself taking steps through the snow. I want to go to the top,” Thompson said. “It’s mind over matter, but my body will tell me what to do.”

Readers can follow the climb’s progress at the Breast Cancer Fund’s blog.

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