Treatment of malignant (metastatic) pheo is a big challenge. Malignant pheo has a very variable clinical course; some patients live with it for many years with high quality of life while some other patients can have a rapid deterioration of their conditions. Malignant pheo is exceedingly rare, making it hard for clinical trials to recruit patients. There have been no approved therapies for malignant pheo so far.
Two recent advances may offer hope. They are both “targeted internal radiotherapies”. The radiopharmaceuticals only go into certain cells of the body, malignant pheo cells in particular (hence “targeted”). The patients would receive intravenous infusions of the radiopharmaceuticals rather than getting radiation from an external source (hence “internal”).
The first one is carrier-free MIBG radiotherapy. We don’t have to go into the technical details of what is carrier-free but this new form of MIBG radiotherapy supposedly deliver more radiation to the tumors. The manufacturer released a press announcement this year, showing the effects of carrier-free MIBG radiotherapy in patients with malignant pheo. Older forms of MIBG radiotherapy have been used for years in clinical practice and in some clinical trials. It is hard to compare the therapeutic effects of the old and new MIBG radiotherapies. Generally the effects are comparable in my eyes. The carrier-free MIBG radiotherapy is tested in a prospective and more controlled manner, thus more convincing.
The second one is PRRT. Although the completed US clinical trial of PRRT is only for carcinoid, PRRT has been used in Europe and Australia for all kinds of neuroendocrine tumors, including malignant pheo. A recently published paper showed that PRRT helps control hypertension and reduce the size of malignant pheo. This study is a retrospective one so it is even harder to compare the carrier-free MIBG radiotherapy and PRRT. My own cursory reading convinces me that they have roughly similar efficacy.
The carrier-free MIBG radiotherapy is seeking US approval. PRRT should be close to approval in the US but will very likely be approved for carcinoid only. Assuming both will be approved eventually, I imagine it will be interesting to how they are used for patients with malignant pheo. The use of PRRT will be “off-label”. Besides efficacy, availability, comorbidities, side effects, cost, and insurance coverage will also be factors that influence the decision to use one over the other. More interestingly, can the two radiotherapies be used in succession? The best indication of the two radiotherapies should be assessed on a case-by-case basis.