An inoperable brain tumor is a tumor in the brain that cannot be safely removed with surgery because of location, size, or other concerns. Alternative treatments are available for such tumors, and they do not necessarily have to be a death sentence. Some grow very slowly, for instance, and a patient may be able to control the growth of an inoperable brain tumor with medications and radiation therapy to live out a normal lifespan.

The determination of whether a tumor is treatable with surgery depends on a number of factors. Every surgeon has a different approach to tumor evaluation and treatment. A tumor one surgeon pronounces inoperable may be considered treatable with surgery by another. Patients may want to consider consulting with several surgeons to get balanced advice about their treatment options, and to make a decision with as much information as possible in hand.

One reason a tumor may be inoperable is because it is in a very complicated location. Brain surgeons cannot access every corner of the brain, or may be concerned that while they could get to the tumor, they might also cause significant collateral damage. The risks for the patient's quality of life may be too great when balanced with the benefits of surgery, and a surgeon may decide a patient has an inoperable brain tumor on the basis of this.

Another concern can be vascularization. Some tumors grow in discrete pockets and they are very easy to remove. The surgeon can find the margins and lift the tumor out intact during the surgery to increase the chance for a positive outcome. An inoperable brain tumor may sprawl, contain tissue that looks a lot like regular brain tissue, or be tangled with blood vessels in the brain. Sometimes this presents too much of a surgical challenge, and it would be dangerous to operate.

An inoperable brain tumor can also be too large for a surgeon to remove safely. The tumor may be wrapped around critical structures in the brain or be too difficult to differentiate from healthy tissue because of the size and level of growth. The surgeon could recommend a partial excision to get as much tissue as possible, but this might also expose the patient to the risk of metastasis by breaking up the tumor and seeding it around the skull.

Other concerns may surround the patient's health. The tumor itself may be operable but a surgeon could worry that the patient will not survive surgery or grueling cancer treatments. In this case, subjecting the patient to surgical trauma would not be ethical, and the surgeon may recommend palliative care and more conservative treatments instead.