When thinking about cancer therapy in recent years, Dorothy’s famous line from “The Wizard of Oz” comes to my mind: “We’re not in Kansas anymore.”

Most fellows in oncology — including myself — begin their training by caring for patients with leukemia because they need a lot of monitoring. Patients with leukemia often are diagnosed with severe bleeds or infections and need treatment urgently.

For decades, treatment for acute leukemia had been largely the same: seven days of a constant drip of drugs through an IV, followed by weeks in the hospital to monitor for complications — kidney problems, infections and other life-threatening side effects.

I spent the first three months of my fellowship in mid-2017 treating patients with leukemia. It was intense, but in the end, I felt comfortable diagnosing leukemia and ordering the initial drugs that would save their lives.

I returned to treating leukemia patients after a four-month hiatus in early 2018. We were admitting a man who we had diagnosed with leukemia, and I was preparing our normal chemotherapy orders.

The pharmacist on our team tapped me on the shoulder and whispered, “Are you sure you want to order that?”

I was confused: Didn’t we treat leukemia the same way we did four months ago?

Turns out that we do not, and she was right: In just four months, the Food and Drug Administration had approved at least two new drugs for acute leukemia, completely changing our treatment paradigm for the disease. Several more drugs would be approved for the disease throughout 2018. Now, instead of treating all leukemia patients the same way, we had different drug options depending on a patient’s genetic and molecular abnormalities.

In short, things had become a lot more complicated.

This is a common story for oncologists and patients with cancer. The pace of change in cancer therapy has been staggering over the past five years. The increased availability of new treatment options — often with better chances of remission and fewer side effects — is good for patients. But for many of them and their physicians, it can be difficult to keep up with all the changes.

This wasn’t necessarily a problem 20 years ago: In a 60-year period, between 1940 and 2000, the FDA approved 72 drugs to treat cancer. But that number more than doubled over the next decade. In 2018 alone, the FDA approved 19 cancer-related drugs.

It would be one thing if the drugs approved in the past 20 years had the same mechanisms and side effects. But we are moving out of an era of generalized cancer drugs and into the era of personalized oncology. New drugs target specific genes or molecules, and many immunotherapies work by stimulating the body’s immune system to fight cancer.

When patients picture themselves getting treated for cancer, many visualize sitting with an IV running for hours, vomiting and losing all of their hair. In the modern era, that is luckily the exception rather than the rule.

Many cancers are treated with a pill, and the majority of patients I see are able to work or go on vacations even during treatment.

The availability of new treatments has upended treatment pathways for common cancers such as melanoma, lung cancer and kidney cancer. And survival rates — even in stage IV cancer — are going up.

But there is a consequence of this renaissance in cancer therapy: Sometimes, we know relatively little about the side effects of the newer therapies we are giving to patients.

I recently met a patient with stage IV melanoma who was being treated with two of the immunotherapies approved for the disease. She had been on the drug for months, and her cancer had shrunk dramatically.

She was a success story.

A few days ago, however, she became extremely fatigued and developed a new headache. An MRI showed that her pituitary gland — a small gland in the brain that secretes hormones — was extremely large because her own immune cells were attacking it.

This was an unusual side effect of immunotherapy, called hypophysitis, and was impossible to predict. Unfortunately, she would need to be on hormone replacement for the rest of her life.

I’ve seen several patients treated with novel therapies who have had similar side effects that seem to come out of the blue.

Access is another problem with newer drugs: Immunotherapies such as CAR-T cells, which have led to long-term remissions for some patients with lymphomas or leukemias, have been approved by the FDA. But they require considerable expertise and experience to use, and thus are only available for certain cancers in a few locations around the United States. Some patients are frustrated that newer drugs are unavailable for their location or their disease.

But perhaps the most challenging aspect about this new era in cancer drugs is convincing patients that they don’t need a novel therapy.

I once saw a man in the hospital with prostate cancer, which had spread to multiple bones, causing him significant pain, and had even involved his liver. He had brought in pages of data on drugs that had been approved within the past five years to treat his prostate cancer. These ranged from cancer vaccines to targeted pills to immunotherapies.

The only problem: Traditional, run-of-the-mill chemotherapy was the best treatment to control his symptoms quickly and prolong his life. I calmly explained why novel therapies, while promising, were not the best treatment for him. He reluctantly accepted chemotherapy. Last I heard, he did well after completing the regimen.

Because of the four-decade investment in the War on Cancer, life expectancy is increasing, side effects are fewer, and cancer can sometimes be a chronic disease rather than a death sentence. As treatment options expand by the day, it is exciting as an oncologist-in-training to learn about these new therapies, while also keeping in mind that existing therapies in cancer can serve some patients.

Ravi Parikh is a fellow in hematology/oncology at the University of Pennsylvania in Philadelphia. Follow him on Twitter @ravi_b_parikh