“The Truth About Cancer” (9 p.m., PBS): Filmmaker Linda Garmon is posing the urgent,

“The Truth About Cancer” (9 p.m., PBS): Filmmaker Linda Garmon is posing the urgent, poignant question, “Why does anyone still die of cancer?” Her husband died of that disease, and in “The Truth About Cancer” she tells his story, as well as offering a progress report on a disease that remains the second-most common cause of death, claiming the lives of more than 1,500 Americans each day. “It’s very much a part of American culture to believe that if you fight hard enough, you can beat cancer,” Garmon says. But with cancer, “your survival depends on the biology of your cancer cells, and whether they are susceptible to state-of-the-art treatment.” Her film investigates when the treatment might be equal to the full threat this disease represents. Then, after the 90-minute documentary, journalist and breast-cancer survivor Linda Ellerbee moderates a half-hour conversation with a panel of doctors, all of whom are also cancer survivors.

“The Big 4-0” (10 p.m., TV Land): A new TV Land reality series follows various 39-year-olds as they move into a new stage of their lives. Each half-hour episode of “The Big 4-0” documents one person greeting that 40th birthday not with a whimper but a celebratory roar. A former pro football player organizes a football game with other ex-NFLers pitted against teammates of a leading college squad. An inveterate thrill-seeker whose horseback-riding accident put him in a wheelchair a dozen years earlier decides he’ll ride a horse again — and skydive. A woman, facing divorce as her 40th birthday looms, gets a surprise party from her friends, and a surprise tropical getaway. The six-episode series premieres with back-to-back half-hours.

“The Real World” (10 p.m., MTV): It’s hard to believe, but “The Real World,” a show that pioneered the reality genre, is about to embark on its 20th season. This time the roommates bring the drama to Hollywood. Let the bickering, back-stabbing and hot-tubbing commence.