Carey Fitzmaurice, a mother of two in Bethesda, Md., was battling ovarian cancer last spring with Doxil, a key part of a chemotherapy mixture that looked as if it was working. But last summer, supplies of Doxil dried up. When we spoke to Fitzmaurice in October, she was on a waiting list.

The drug never came through. She continued therapy without it. Since then, the markers for her cancer have risen. And on Wednesday, she learned that doctors had found new tumors. There's no way to know for sure, but Fitzmaurice believes that if she had been on Doxil, "I wouldn't be dealing with ovarian cancer right now."

Shortages of Doxil and other drugs used to be rare. But they've quadrupled since 2005, reaching 250 last year. Many are old, reliable and often cheap drugs used to treat cancers, anesthetize patients for tests or surgery, or intravenously feed those who can't eat.

Though the Food and Drug Administration has found better ways to alleviate shortages and some makers are providing the FDA with earlier warnings, the problem persists. This year, there have been 42 shortages. Although that's fewer than at this time last year, if you're the patient who needs an unavailable medication, the decline is of little consolation.

How could this happen in 21st century America, with drugs that were readily available for years? And why is it mostly inexpensive, old reliables?

Many of the theories are focused on a half-dozen companies that supply 90% of the generic drugs known as "sterile injectibles." Since 2010, several have shut down production lines for repairs after the FDA found problems. Getting another company to gear up to replace lost capacity is slow and expensive. All true.

The trouble with these theories and the patchwork solutions they spawn is the focus on symptoms, not the root cause. The most plausible explanation is all but ignored. The free market, which usually takes care of shortages, isn't working. Normally, prices rise with shortages, and an enterprising company jumps in to make a buck.

In fact, the opposite has happened with some of these drugs, especially the sterile injectibles used to treat cancer. From 2006 to last year, their prices dropped by a third.

One reason for shortages, according to prominent health care experts and economists, is a provision in a 2003 Medicare drug law that limits price hikes for drugs sold to hospitals and doctors (rather than directly to patients) and reimbursed by Medicare and private insurers.

The provision was a well-intentioned reform meant to deal with inflated prices that manufacturers had been charging for years. But an unintended consequence has been life-threatening shortages. Ali Yurukoglu, of the National Bureau of Economic Research, concluded that the lower prices gave manufacturers less incentive to invest in additional maintenance or capacity, or to enter the market.

The Generic Pharmaceutical Association, which represents the makers, denies money has anything to do with the shortages. That reasoning flies in the face of logic. Most in Congress are avoiding the obvious, too, pushing fixes that ignore the core problem. But Sen. Orrin Hatch, R-Utah, has drafted a measure to revisit the 2003 Medicare law and use market forces to avert shortages.

Medical science has produced powerful drugs to vanquish cancer in some cases or at least to hold it in check in others. When treatments exist, and people like Carey Fitzmaurice must go without, it's past time to find out why and fix it.

This article was published and distributed by USA Today.