The cost of Keytruda, a cancer medication produced by Merck & Co., can vary depending on several factors such as the dosage, treatment duration, and the patient's insurance coverage.

According to GoodRx, the average retail price for a 100mg/4mL vial of Keytruda intravenous solution is around $13,445, as of October 2021 [1]. However, it is essential to note that this price can fluctuate and may not be accurate for every situation.

Additionally, DrugPatentWatch.com reports that Keytruda's patent expiration date is in 2028 [2]. This information suggests that generic versions of Keytruda may become available in the United States market after 2028, which could potentially lower the cost of the medication.

In summary, the cost of Keytruda can be approximately $13,445 for a 100mg/4mL vial, but the price may vary depending on individual circumstances. After 2028, generic versions of Keytruda may become available, potentially reducing its cost.

Sources:
[1] <https://www.goodrx.com/keytruda>
[2] <https://www.drugpatentwatch.com/drugs/keytruda>