2

Radiation therapy (RT) is far less barbaric than it sounds. Yes, at its core, it is zapping a patient’s body with high-energy photons, electrons, protons or other modalities, but the delivery is extremely precise and the dosage is carefully determined based on the target area, organs at risk (OARs), and the tolerance of the tissues therein. The precision of the equipment is such that it can deliver radiation to the target area ±~1 mm and 1^o of rotation. Compared to other methods of disease treatment, namely surgical resection and chemotherapy, which can affect substantial amounts of proximal healthy tissue and have widespread systemic effects respectively, this seems like the best example of precision medicine in an oncologist’s toolbox.

This week I have seen numerous patient consults, follow-ups, and planning sessions, largely for patients with low and high grade gliomas, brain- or bone-metastatic cancers, or benign brain tumors. For patients with benign tumors like meningiomas and schwannomas, RT is used either alone or in conjunction with surgical resection, and is meant as a definitive, curative treatment whose purpose is to ameliorate any existing neurological symptoms caused by compression of brain tissue. It is also meant to prevent future neurological symptoms from developing. These tumors tend to be very slow growing, on the order of 1 mm per year, so treatment is not urgent if the patient does not present with symptoms. Generally, for patients with metastatic disease or gliomas, the treatment is palliative – intended to slow or stop growth of existing lesions and limit any associated pain or neurological symptoms. Radiation therapy does a good job at palliation.

In a tumor board this week, a patient was presented with an arachnoid cyst, a cerebrospinal fluid filled cyst formed in one of the three meningeal layers near the brain stem. The cyst was surgically resected and sent to pathology where a parasitic flat worm was found. Additionally, neoplastic cells were identified, but the cells did not appear to come from a brain cell lineage. The patient did not have any other tumors, so this could not be a metastasis. A google search led the pathologist to a paper published several years ago in which a patient with advanced HIV presented with multiple neoplasms that, when genotyped, had no human DNA in them. Indeed, in our case, when the sample was stained for human cellular markers, it came back negative. The cancerous lesion identified in this patient’s brain was actually an arachnoid cyst caused by a parasitic flat worm that had cancer.

The worm’s next of kin have been instructed to seek genetic screening.