It was a randomized study. And in order to be eligible for randomization, patients needed to have a PSMA positive finding on a PSMA PET CTA. That's a gallium-68 PSMA PET CT. So these patients, heavily pretreated patients, who had metastatic CRPC underwent this screening PSMA PET. If they were positive and met other eligibility criteria, they were randomized on a 2 to 1 basis to receive the physician selected standard of care with or without lutetium-177-PSMA-617.
And when I say the physician selected standard of care, that needed to be a safe combination. So that could not include chemotherapy, radium 223, immunotherapy, or other treatments for which we really don't have safety data of those agents or classes of agents in combination with a new drug like lutetium-177-PSMA. Remember, though, that most of these patients really had to be deemed by their physicians not to be chemotherapy candidates before entering this trial. And the patients also had to have already progressed on either one or two prior chemotherapy agents.
The treatment with lutetium-PSMA was given for four cycles, which could be expandable to six if the patients were responding and had residual disease. And those treatments are given every six weeks. For the primary endpoint of overall survival, the improvement in the risk of dying was 38%. That's a hazard ratio 0.62. Median overall survival was improved from 11.3 months to 15.3 months. And the p value on that was less than 0.001.
For the other endpoint, the other primary endpoint, that is RPFS, the risk of progression was decreased with treatment with lutetium by 60%. And that's represented by a hazard ratio of 0.4 with a p value of less than 0.001. And the improvement in median RPFS was an improvement from 3.4 months to 8.7 months with the addition of lutetium-PSMA on top of the standard of care.
So it's a very positive trial. Those two primary endpoints were reinforced by the secondary endpoints in favor of lutetium. So 9% of patients had a complete response on scans relative to 0% in favor of lutetium. 42% had a partial response on scans versus 3.1% in favor of lutetium. And then, in terms of patients who had a 50% or greater decline in PSA, 46% achieved that decline with lutetium, and 7.1% achieved that PSA decline just on the standard of care alone. So whether you're talking about PSA, scans, RPFS, or overall survival, the combination of lutetium-PSMA-617 with the standard of care was superior to the standard of care alone.
When we talk about safety for these agents, there are really three main domains that we are concerned about. And when I speak about these agents, I'm talking about PSMA directed radioligand therapy. For all radioligand therapy, because it does involve systemic radiation, one of the main side effects is going to be bone marrow suppression. And so for high grade bone marrow suppression, we saw a rate of about 23%.
Now, that comes down to in terms of significant things to look for in that general category, a high grade anemia rate of 13% and a high grade thrombocytopenia rate of 8%. In terms of a second class of concerns with PSMA directed radioligand therapy, xerostomia is another concern, because PSMA is expressed in both the salivary and lacrimal glands.
Here, we saw a 39% xerostomia rate overall for all grades, and none of it was high grade. And then finally, we did see a 39% nausea and vomiting. This is generally speaking infusion related. Only 1.5% of that was considered to be high grade. And then, in terms of kidney impact, we saw very little in the way of kidney impact over and above what was seen in the standard of care arm as well.
There's a clinical trial that's currently open and enrolling, testing this agent in men with metastatic CRPC, who have not received chemotherapy yet. And then there is another trial that's activating now of using this agent in men with castration sensitive metastatic cancer. And that trial is a randomization of ADT, plus the antigen pathway inhibitor of the physician's choice, plus or minus lutetium-177-PSMA-617.
In addition, combinatorial strategies are being pursued to combine this agent with others, again, to see if perhaps we can optimize the treatment effects seen by combining it with other agents. Well, I think that both patients and oncologists should feel very optimistic and excited by the results of this trial. It introduces to prostate cancer the first tumor directed radioligand therapy as a drug class that improves survival in a patient population that has few other treatment options.
And it introduces as well the possibilities of new combinations and new treatment opportunities even earlier in the disease as the clinical trials open up and are further explored. So it's a new treatment opportunity for patients, a new drug class for prostate cancer. And generally speaking, that's good for everybody, especially for the patients who so desperately need new therapies for this situation that they have.