This weekend, nearly 7,000 bicyclists will take to the streets for the 45th year of the Pan-Mass Challenge.

Founder Billy Starr remembers the first year of the challenge, an annual fundraiser that benefits cancer research and treatment at the Dana Farber Cancer Institute. At the time, the plan was just a single event.

“In 1980, there was no plan for 1981,” he recalled. “This was an expression I needed to make. I was able to, in my own mind, coalesce that I was going to do an event by myself to getting a group of people to ride with me.”

Some of those people promised to participate or volunteer the following year. Others told him how much the challenge meant to them. Those positive responses convinced him to make it a recurring activity.

“I always thought that my work should have value and meaning,” he said. “And from that moment on ... I just applied myself and step by step. You know, here we are.”

The fundraising activity is the largest single contributor to the Dana-Farber Cancer Institute. This year, the Pan-Mass Challenge hopes to raise $75 million through rider sponsorships and general donations. They hit a major milestone in July: $1 billion.

“So we’re on to the second billion!” Starr said. “And that’s pretty exciting, that which took 45 years — I expect — will take 10 to 13 years to raise the second billion.”

Starr said the spirit of the event remains the same today as it was in 1980.

“We’re a bigger band of brothers and sisters than when we started, but this has been a pretty big event since the early- [to] mid-90s,” Starr said. “And yes, it’s at another level. We now have 16 routes.”

Most of the participants will take on the two-day ride from Sturbridge or Boston to Bourne, and then onward to Provincetown. And while the forecast isn’t ideal summer weather, Starr isn’t concerned.

“It is a summer rain — trust me, with the heat and humidity, a little rain’s not a bad thing,” he said. “And a little rain is not going to deter the mission.”