A new immunotherapy schedule in addition to first-line hormone therapy for metastatic breast cancer patients in a state of clinical benefit during hormone therapy.

Acquired resistance occurs in metastatic hormone receptor-positive breast cancer patients. The addition of interferon beta/interleukin-2 immunotherapy to first-line salvage hormone therapy (HT) prolonged progression-free (PFS) and overall survivals (OS) in 26 patients, as compared with 30 historical controls and literature data. This was a 2 : 1 ratio case-control retrospective observational study. The cases were from an open pilot study, started in 1992, and controls were recruited in 2006. The planned mean follow-up time was the time at which more than 80% of controls progressed. The median PFS was significantly longer in the cases than that in controls, 33.1 (95% CI 24.5-41.8) vs 18 (95% CI 12.1-23.8) months (p < 0.0001). Also, median OS was significantly longer in the cases, 81 vs 62 (95% CI 48.1-75.9) months (p < 0.0029). When analysis of the 2 groups was adjusted for the disease-free interval (DFI), hormone receptor status, HER2, site of metastases and molecular-targeted therapies, the hazard ratio for PFS and for OS in the cases increased from 2.347 to 3.090 and from 1.874 to 2.147, respectively. This occurred in spite of the higher proportion of controls (82% vs 7.1%) treated with aromatase inhibitors (AIs), while selective oestrogen receptor modulators (SERMs) were given to 92.9% of the cases and to 18% of the control group (p < 0.0001). Immunotherapy significantly prolonged PFS and OS during conventional first-line HT. A multi-centre randomised clinical trial is advised to enter this immunotherapy into clinical practice. KEY MESSAGES: • Acquired resistance occurs in metastatic endocrine-dependent breast cancer patients. • Interferon beta-interleukin-2 immunotherapy added to first-line salvage hormone therapy prolonged progression-free (PFS) and overall (OS) survivals in 26 patients of a pilot study as compared with 30 historical controls. • In this 2:1 ratio case-control prospective observational study, the PFS median time was significantly longer in the study group than that in controls, 33.1 (95% CI 24.5-41.8) vs 18 (95% CI 12.1-23.8) months (p < 0.0001). • Also, the OS median time was significantly longer in the study group, 81 vs 62 (95% CI 48.1-75.9) months (p < 0.0029).