Trodelvy is neither traditional chemotherapy nor immunotherapy. It belongs to a newer category called antibody-drug conjugates (ADCs), which combine elements of both approaches: a targeted antibody that seeks out cancer cells and a chemotherapy drug that kills them. Think of it as a guided missile rather than a carpet bomb. The antibody locks onto a specific protein on cancer cells, then delivers a potent cell-killing payload directly to the tumor.
How Trodelvy Actually Works
Trodelvy has three components working together. The first is a lab-engineered antibody designed to recognize a protein called Trop-2, which sits on the surface of many cancer cells. The second is a cancer-killing chemical called SN-38, which is the same active ingredient found in certain traditional chemotherapy drugs. The third is a chemical linker that holds the antibody and the drug together until they reach the tumor.
Once infused into your bloodstream, the antibody portion circulates through the body searching for cells that display Trop-2 on their surface. When it finds them, it latches on and gets pulled inside the cancer cell. The linker then breaks apart, releasing SN-38 directly inside the cell, where it interferes with the cell’s ability to copy its DNA and ultimately kills it. Trop-2 is overexpressed in a wide range of cancers and is linked to more aggressive tumor behavior, which makes it a useful target.
Why It’s Not Chemotherapy or Immunotherapy
Traditional chemotherapy floods the entire body with cell-killing drugs. Those drugs attack any rapidly dividing cell, cancerous or not, which is why side effects like hair loss and low blood counts are so common. Trodelvy still carries a chemotherapy drug, but concentrates it at the tumor site rather than spreading it everywhere equally. This is what makes ADCs a distinct category: they aim for a more targeted approach than standard chemo.
Immunotherapy, on the other hand, works by training or unleashing your own immune system to recognize and destroy cancer. Checkpoint inhibitors like pembrolizumab (Keytruda) are the most well-known examples. Trodelvy does not activate the immune system. It kills cancer cells directly through its chemical payload. The antibody portion is used for navigation, not immune activation.
That said, Trodelvy can be combined with immunotherapy. A recent trial called ASCENT-04 tested Trodelvy paired with pembrolizumab as a first-line treatment for metastatic triple-negative breast cancer. The combination improved progression-free survival compared to standard chemotherapy plus pembrolizumab, suggesting ADCs and immunotherapy can complement each other.
What Trodelvy Is Approved to Treat
Trodelvy currently has two FDA-approved uses, both for advanced breast cancer that has spread or can’t be surgically removed. The first is metastatic triple-negative breast cancer (mTNBC) in patients who have already tried at least two other treatments. The second is hormone receptor-positive, HER2-negative metastatic breast cancer in patients who have received hormone therapy and at least two additional treatments.
Trodelvy previously held an accelerated approval for advanced urothelial cancer (bladder cancer), but Gilead Sciences voluntarily withdrew that indication in late 2024, and it was removed from the product label in November of that year.
How Well It Works
In the TROPiCS-02 trial, which enrolled patients with hormone receptor-positive, HER2-negative metastatic breast cancer, Trodelvy extended median overall survival to 14.4 months compared to 11.2 months with standard single-agent chemotherapy. Progression-free survival, the time before the cancer started growing again, was 5.5 months versus 4.0 months. These differences were statistically significant, meaning they were unlikely to be due to chance.
For triple-negative breast cancer, the ASCENT trial showed similar advantages over standard chemotherapy in patients who had already been through at least two prior treatment regimens. Those results were strong enough to make Trodelvy a recommended second-line option for mTNBC.
What Treatment Looks Like
Trodelvy is given as an intravenous infusion on days 1 and 8 of a 21-day cycle. That means two infusion visits roughly a week apart, followed by about two weeks off before the next cycle begins. Treatment continues for as long as the cancer responds and side effects remain manageable.
Side Effects to Expect
Despite its targeted design, Trodelvy still carries significant side effects because SN-38 is a potent chemotherapy agent. The drug carries FDA black box warnings for two serious risks: severe drops in white blood cell counts (neutropenia) and severe diarrhea.
In clinical trials, neutropenia occurred in 54% of patients, with 13% experiencing the most severe grade. Febrile neutropenia, where the low white cell count triggers a fever signaling possible infection, occurred in about 6% of patients overall and 9% of those with triple-negative breast cancer. This risk requires regular blood monitoring throughout treatment.
Diarrhea affected about 63% of patients, though severe cases (grade 3 or 4) occurred in roughly 9%. Nausea was even more common at 67%, and nearly half of patients experienced vomiting. Allergic reactions occurred in 35% of patients, though severe reactions were rare at around 1%. These side effect rates are broadly similar to what you’d see with traditional chemotherapy, a reminder that while the delivery system is more targeted, the payload itself is still a powerful drug.
Where ADCs Fit in Cancer Treatment
Antibody-drug conjugates represent a growing middle ground between the blunt force of chemotherapy and the immune-based strategy of immunotherapy. Trodelvy is one of several ADCs now approved for different cancers, and the category is expanding rapidly. For patients with advanced breast cancer who have already been through multiple treatments, Trodelvy offers a targeted option that has demonstrated real survival benefits over conventional chemotherapy. It doesn’t replace immunotherapy or traditional chemo but adds another tool, one that borrows from both worlds without fully belonging to either.