Yesterday I wrote about Neulasta, the chemo immune support drug billed at $15,000 a pop. But Neulasta is prescribed for a limited period. Today I want to dig into a drug that is taken for a much longer time: Zoladex.

If you have hormone-receptor-positive breast cancer, which 80% of breast cancer patients do, part of long-term treatment involves shutting down estrogen production in the body. The best way to do this, currently, is to take an aromatase inhibitor (AI) for five to ten years.

If you are premenopausal at the time of treatment, taking an AI is not enough. You also need ovarian suppression. There are three ways ovarian suppression can be achieved: removing the ovaries surgically, radiating the heck out of them, or taking a drug. The first two are very permanent, and since ovarian suppression can have a lot of side effects, are not an ideal first step. That leaves drugs.

As far as I can tell, there are two main drugs used for this in the U.S., Lupron and Zoladex; I am on the latter. Now, chemotherapy threw me directly into menopause, as it does for most women my age (45 at the time). But this is not guaranteed to stick, hence the Zoladex. Once you start Zoladex, you don’t know if menopause would continue without it, so you have to keep taking it. The estimate was for five years.

That brings us to the cost. Aromatase inhibitors are generic and pretty cheap. Apparently you can get one for $30 a month at Costco. (Though see this crazy story from 2013 about pricing.)

But Zoladex is administered as an every-four-week injection that retails around $900 a pop. The hospital bills $2600: $2200 for the drug and $358 for a nurse to inject it. Insurance pays $966 for the drug and $88 for the injection. So someone is paying about $13,000 a year for me to take this drug. For five years. That’s $65,000.

So why is Zoladex so expensive? It was patented in 1976, and first approved in 1989. Why does a drug nearly as old as me still cost so much?

Researching this sent me down a bit of a rabbit hole. As with Neulasta, it’s complicated. And as usual, the overarching conditions of no government-sized entity negotiating prices in the U.S., and cancer drugs in particular being extra expensive, are really important. Other relevant issues are providers’ hesitance to switch from a known drug, and everyone’s insulation from prices in decisionmaking.

There is also an issue with “patent thickets,” in which manufacturers patent as many things associated with the drug as possible in an effort to fend off competition, or at least slow it down in litigation. The 12 biggest selling drugs are protected by an average of 71 patents each, giving them an average of 38 years without generic competition.

But there are some specific reasons that Zoladex and some of its peers have no meaningful competition after so many years. Take what follows with a bit of caution, because the patent stuff gets very complicated and I’m not sure I have all the details right. But the actual chemical compound of goserelin, the generic compound in Zoladex, went off patent in 2005. What still appears to be patented—until 2021?—is the special auto-injecting syringe.

Apparently, this is a more general issue. Unlike a biosimilar drug, a generic version of Goserelin would not have to go through a complex regulatory process to demonstrate effectiveness. But injectables (most cancer drugs) and other sustained release drugs can have delivery mechanisms patented and are extra hard to copy. So manufacturers innovate on delivery systems, patent those, and hope it will throw up enough barriers to fend off competition for a longer period of time.

And it’s working. While there is an alternative drug to Zoladex, Lupron, it has similar issues. It is twice as expensive as Zoladex, despite having been patented in 1973 and on the market since 1985. (It’s still under patent as well.)

The result is that the inflation-adjusted price of Zoladex has increased 50% in the last 20 years, despite the fact that its active ingredient has been off-patent for fifteen.

And while, to the uninitiated, $13,000 a year seems like a lot to pay for a maintenance drug, this isn’t even all that much in the world of Cancerland. More on that next.