For two decades he has headed the American Federation of Teachers, and he has no plans to retire. He talks of the cancer, which was first diagnosed two years ago and reappeared last April, chiefly in terms of its impact on his business calendar.
Now, as he waits to see what "magic potion" the doctors come up with next, the 68-year-old former teacher works mostly from his home in New York, by telephone, fax, and modem. So far he's not had any of the worst side effects of chemo, he says, the "long list of horrors" that other patients have encountered.
Stated in its most simple terms, Shanker's achievement is this: during his tenure at the AFT, its membership has gone from 50,000 to 950,000, bucking a national trend of shrinking union clout. With a celebrated confrontation with New York's school authorities in the 1960s, he introduced the practice of collective bargaining for American teachers.
At the same time Shanker has taken the AFT from simple demands for better pay and working conditions - such as lunch breaks - and swung it behind centrist demands for high quality education. He is an outspoken backer of a national curriculum to raise standards, of the power to remove disruptive children, and of streaming and tracking in classes. He supports recognising outstanding "lead teachers", and has endorsed publicly funded, but independently run "charter" schools.
As schools have moved from the factory model, he says, so unions have to adapt their own role, and he likes to defy the label of left or right. The two best-known anecdotes about Shanker are that comic Woody Allen, in a throwaway line in his film Sleeper, cast the union boss as the nuclear bomb thrower who destroyed civilisation; and that a few years later, Ronald Reagan invited him for lunch.
His tenure at the AFT, though hugely successful from an organising standpoint, has come at a time when middle-class and particularly white parents took flight en masse from urban public schools. "There are more and more people who are unhappy with the public schools," he said. "There is more and more feeling that if public schools can't do the job, that pupils should be able to escape and go to private schools."
But Shanker draws the line at voucher systems being tested in some US school districts in the name of school choice. That, he says, is a reform too far that threatens to break up the public school system and Balkanise American education. It would also extend to religious schools, institutions where there are no rights to unionise.
Al Shanker's parents were Yiddish immigrants from near Pinsk, then part of Czarist Russia and now part of Belarus. His mother worked 70-hour weeks in the New York garment industry, where she joined the Amalgamated Clothing Workers union, and his father, who had trained as a rabbi and fought for the Czarist army, turned newspaper deliveryman.
Until he went to school he spoke scarcely a word of English. But he won entrance to one of New York's top public high schools, and after rejection by Harvard, went on to the University of Illinois.
His up-by-the-bootstraps tale seems reflected in an approach that classrooms should be devoted to hard work, achievement, and discipline rather than fudging standards in the name of inclusiveness.
He became a teacher in 1952. Seven years later, he was a full-time organiser with the New York Teachers' Guild, affiliated with the AFT. At the time there were about 50,000 teachers in New York, with only 2,500 members of the guild; most were scattered between a hundred-odd groups that were "essentially social clubs to give outgoing presidents a gift," he said.
Undaunted by the numbers, in 1960 the union called a strike to demand collective bargaining. "It was mostly guts," Shanker said. In the midst of the baby boom, organisers calculated the city could not afford to lose even a few thousand teachers. They were right. In a subsequent referendum, the union was the overwhelming choice of teachers to represent them at the bargaining table.
The AFT, where Shanker was elected national president in 1974, still has its powerbase on the East Coast. Outside New York and Florida, it is chiefly represented in the urban schools. The rival National Education Association is twice the size, but it is under such pressure from Shanker's AFT that it has moved from being a largely docile professional association to an active union in its own right.
Shanker's influence on education, it is widely said, is huge. Appointed to a presidential commission by George Bush, he was also an adviser to the incoming Clinton Administration. Guests at the 25th anniversary party for his column, of which Shanker has written more than a thousand, included Senator Edward Kennedy, secretary of state for education Richard Riley, and conservative columnist and former Reagan aide Linda Chavez.
Every Sunday Shanker's "Where we stand" appears as a paid advertisement on the same page of the New York Times' "Week in Review" section, and in The New Republic magazine. It guarantees that his views are made known to doers and thinkers, though it costs the AFT an estimated $500,000 (Pounds 320,000) a year.
In columns this October, Shanker returned to familiar themes. He attacked the "big myth" that vouchers will get poor children into elite schools, and registered outrage over a court's decision to revoke the suspension of a New York teenager caught bringing a gun to school.
As he prepares for his next round of therapy, Shanker says he has no plans to retire. "A lot of leaders stay longer than they should," he noted, but in polling his colleagues and friends, he senses no need to make way for a successor. The AFT "was there before I was there, and it will be there after I'm there," he said. "But I've made my mark on it."