SBRT and immunotherapy for metastatic lung cancer
Metastatic non-small cell lung cancer (NSCLC) is a common presentation of lung cancer. Lung metastases develop in 20–54% of cancer patients. Aggressive management at this stage can improve survival and the Quality of Life (QOL).
SBRT (stereotactic body radiation therapy) and immunotherapy are two promising modalities for the treatment of metastatic lung cancer.
SBRT is a non-invasive procedure that delivers high doses of radiation to target lesions, while sparing the surrounding normal tissues. On the other hand, immunotherapy is a treatment that engages with the body’s own immune system to fight cancer.
Promising results from recent studies have shown that SBRT and immunotherapy, when used together, are both safe as well as effective. This dual approach improves the survival outcomes offering a lifeline to patients with metastatic NSCLC. Three to five fractions of high-dose radiation therapy (≥5 Gy/fraction) can stimulate tumour antigen release making these lesions to be recognized by the immune system. This, in turn, enhances T-cell infiltration in the irradiated lesions.
Benefits of this combination therapy is attributed to the synergistic effects that lead to an enhancement of the antitumor immune response. It has been suggested that the mechanism of this synergy is based on the premise that SBRT changes the tumour environment so that more tumor T-lymphocytes, that can attack and kill tumor cells, are produced. While immunotherapy enhances and amplifies the effect of radiation-induced cell death, preventing tumor regrowth
Several clinical trials have shown that SBRT can be combined with immunotherapy, especially checkpoint inhibitors. Immune checkpoint inhibitors block proteins on the surface of cancer cells or immune cells that prevent the immune system from attacking the cancer. The dual therapy was found to be safe and doubled the response rate when compared to drug alone in patients with metastatic NSCLC.
SBRT is administered by expert radiation cancer specialists. Prior to the procedure, a precise map of the extent of the tumor is done. A practice session may be carried out initially to finalize the tumor treatment area taking into consideration the movement of the lungs. During the actual procedure, the patient is advised to remain still and breathe normally. A week or so later SBRT can begin depending on the size and location of the tumor.
It is an out-patient procedure that does not require anesthesia. Up to five such treatments are usually undertaken, each lasting about 30 minutes or so. Most patients will not experience any side-effects except for some minor fatigue & nausea.
Immunotherapy drugs can be given as injections into a vein (intravenous or IV) every few weeks. Immunotherapy can also cause allergic reactions or autoimmune reactions, where the immune system attacks healthy organs and tissues. Doctors need to monitor the patient’s condition closely during and after treatment.
Ongoing trials are testing the optimal timing, dose, and sequence of SBRT and immunotherapy for different stages and subtypes of NSCLC for better clinical outcomes.