Runner John Ounao cries when he finds friends after explosions...

Runner John Ounao cries when he finds friends after explosions rocked the finish of the Boston Marathon in Massachusetts. (April 15, 2013) Credit: Getty Images

The city of Boston will live with the reverberations of the marathon bombing for years -- just as New York region residents have with 9/11.

A reminder surfaced this week when a federally sponsored study of nearly 21,000 World Trade Center rescue workers found a 15 percent increased incidence of cancer.

That study, coming more than a decade after the World Trade Center attacks, catalogs with awful clarity one lingering effect: Greater than expected rates of thyroid, blood, lymph and soft tissue cancers among responders from four states who pushed through rubble with little thought about toxins that medical and other researchers later would find.

Terrorism has been defined as using violence to intimidate a society as a way to further some political or social objective. Intimidation? It didn't happen in New York. Or in Boston.

Neither city allowed itself to be cowed. That should not have come as a surprise to Dzhokhar Tsarnaev, a naturalized U.S. citizen in the last year of his teens, who, authorities said, boasted of his role in attacks that killed a child, two women and a police officer.

The threat of terrorism continues, with too many others seemingly eager to follow in the footsteps of Tsarnaev and his older brother, Tamerlan, who was killed in a police shootout after the bombings.

The selfless response of residents, police and rescue workers in Boston, as in New York, shows that Americans will not shy away from the challenge.

In Boston, ripples from the attack are just beginning. In funerals for victims this week, the shock and grief of families mirrored the feelings of those who lost loved ones on 9/11. None of them will ever be the same.

In Boston, thankfully, there are plentiful survivors, some of whom lost limbs. Their road to recovery -- physically, mentally and financially -- will be hard.

On Tuesday, the number of injured was upped to more than 250, including victims who sought help for less serious injuries, including ears that would not stop ringing or puncture wounds later discovered to have been caused by shrapnel from two homemade pressure-cooker bombs.

Authorities have yet to determine a definitive reason for the brothers' decision to go on a gun and handmade bomb-making spree.

But federal and other authorities are certain to keep pushing to find out why, even as Congress pushes to determine whether the FBI dropped the ball after the Russian government made inquiries about Tamerlan Tsarnaev.

Has it been only a week and two days since the Boston attack? And was it just Monday that Canada announced arrests in a foiled al-Qaida-supported plot to bomb a passenger train? No matter. After more than a decade of dealing with terrorism, the nation continues to adjust to an increasingly dangerous world.