Thousands of cyclists from near and far put on their riding shoes early Saturday morning for a good cause: to raise money for cancer research.

And after some rode nearly 90 miles and others more than 100, they will be hopping on their bikes again Sunday as the 43rd annual Pan-Mass Challenge continues.

Roughly 6,400 cyclists are participating in this weekend’s bike-a-thon fundraiser, as PMC looks to meet its ambitious goal of raising a record-breaking $70 million for Dana-Farber Cancer Institute.

PMC raises more money for charity than any other single athletic fundraising event in the country.

Participants, waking up before dawn Saturday, either started in Sturbridge or Wellesley before finishing their long, grueling hauls in Bourne. Sunday’s rides will end in Provincetown or at Patriots Place. Some riders will be completing out-and-back loops in Wellesley.

PMC donates 100% of every rider-raised dollar directly to Dana-Farber to fund lifesaving cancer research, treatment and patient care. The organization is Dana-Farber’s single largest contributor, accounting for more than 60% of the annual revenue at the Jimmy Fund. Last year, the PMC raised $69 million, bringing its 43-year contribution to Dana-Farber to $900 million.

One of the thousands of riders participating this year is former NFL QB Alex Smith, competing in his first PMC.

The bike-a-thon fundraiser has become quite personal for Smith. Last year, his daughter Sloane was diagnosed with a very rare brain tumor.

He rode from Sturbridge to Bourne on Saturday and is waking up on Sunday with likely sore legs to finish the journey to Provincetown. His longest ride during training had been 35 miles, he told the Herald this week.

“This will definitely be a big step up for me,” Smith said, adding that his emotions for the weekend ranged from “excited” to “nervous and anxious.”