In the second paragraph of his 1995 novel Sabbath's Theater, Philip Roth drops in a phrase about "the prostate enlarging" within his aging protagonist. That line just might be the transitional one, or the prophetic one, in the remarkable final chapter of Roth's career. His magnificent books over the past dozen years, particularly the trilogy of American Pastoral, I Married A Communist and The Human Stain, form a literature inspired by prostate cancer. The connection has only become more explicit with the new novel Exit Ghost, in which Roth's fictional stand-in Nathan Zuckerman has been rendered impotent and incontinent by surgery for the disease. In interviews over the years, Roth has insisted that his knowledge of prostate cancer derives from his friendship with a group of peers in their 60s and 70s, whose lives were "blighted by that savage disease," as he put it recently in a discussion with the Washington Post. Given the acuity of Roth's physical descriptions, however, and his longtime fondness for playing postmodern games with his identity (Operation Shylock, anyone?), I have to assume this malignant muse visited the author himself. The literary result goes well beyond Roth's ability to describe symptoms and treatments of prostate cancer with the precise sort of detail he brought to the process of glove-making in American Pastoral. A writer ruled by his sexual organ for much of his career, Roth has become a deeper and greater observer of life once he confronted the weakening or removal of the gland that controls its function. Roth has not suddenly stopped writing about sex, his staple, though the most intense scenes of sex are now those of remembered passions, like the septuagenarian Coleman Silk recalling his Greenwich Village lover of a half-century earlier in The Human Stain. Rather, without the lived experience of all sex all the time, the Rothian nirvana, the author has taken in the rest of the world, or at least the rest of postwar America. WHICH BRINGS me back to Sabbath's Theater, the pivotal book in the process. Few novels in the Roth oeuvre better capture the duality in his work of brilliance and lunacy. In scenes that anticipate aspects of The Plot Against America, Roth heartbreakingly describes Mickey Sabbath in his waning years still struggling with the death of his beloved older brother in World War II. Yet the book reaches its climax, pun not entirely unintended, when Sabbath visits his longtime lover, one of Roth's recurring and unbelievable whores-with-a-heart-of-gold, on her cancerous deathbed. Her tender departing memory - there is no tactful way to put this - is of a lovemaking session that culminated in her drinking Sabbath's urine. Something in the real or researched or imagined experience of prostate cancer, the disease only hinted at in Sabbath's Theater, increasingly turned Roth's gaze from the bedroom out the window. In an interview with Amazon.com about Exit Ghost, Roth said that Zuckerman, in the aftermath of prostate surgery, is "removed from the sexual arena himself, and therefore becomes an observer of it in others." For once, Roth may have undersold himself. Zuckerman actually has observed a great deal more than the others' unafflicted sex lives. In the trilogy, the body part that works hardest for Zuckerman is his ear. Roth introduces the diminished Zuckerman early in each book to be the confessor and in turn the Scheherazade of the stories of the central characters - Swede Levov, whose daughter got caught up in the violent fringe of the anti-Vietnam War movement in American Pastoral; Ira Ringold, whose naive, idealistic dabbling in Marxism leads to his blacklisting in I Married A Communist; and Coleman Silk, a black man who passes for white in his effort to transcend race itself in The Human Stain. Those books share a large historical vision with The Plot Against America. In that fictional memoir, Roth depicted the plight of his family and their fellow Jews in Newark after the Nazi sympathizer Charles Lindberg defeated Franklin Roosevelt for the presidency in 1940 and brought a version of fascism to the United States. Probably no book of Roth's has less sex in it. Exit Ghost shares its style more with Everyman, an evocative and almost delicate mediation on aging and waning powers. And in The Dying Animal Roth tried, not surprisingly with less success, to imagine his way into the female analogue for prostate cancer - breast cancer that mutilates the former lover of David Kepesh, another of Roth's doppelgangers. WITH ZUCKERMAN, Roth is assured and vivid and compassionate in his description of the ravages of prostate cancer and surgery. He describes Zuckerman in Exit Ghost as "a man bearing between his legs a spigot of wrinkled flesh." Later in the same sentence, he likens the penis to "the end of a pipe you see sticking out of a field somewhere, a meaningless piece of pipe that spurts and gushes intermittently." In the real world, where even the prime minister now has been diagnosed with prostate cancer and is anticipating surgery, it is worth pointing out that the operation quite often spares the nerves that control continence and sexual function. Even when those nerves are harmed, there are mechanical or chemical ways to return some degree of sexual operation. But whether the absolutely bleak outcome for Zuckerman is a fictional trope or a reflection of his creator's experience, it has worked wonders for Roth as a novelist. It forced him away from a favorite subject, or put that subject into perspective, and so opened him to bigger, broader issues. And knowing the real suffering of cancer and its harsh cure has moved him past the unconvincing, whiny portrayal of suffering at the hands of smothering mothers or harridan wives. Roth has developed an empathy largely absent in his earlier novels. Speaking as a devoted reader, and speaking from personal experience as well, I wouldn't wish prostate cancer on anyone. But perhaps for Roth it has been Beethoven's advancing deafness - a terrible curse that somehow liberated the highest art.