Years before his death, Hammerstein developed a slow-growing mass below his left ear but declined to seek medical advice. In January 1943, Prof. Dr. Ferdinand Sauerbruch informed him that he had cancer, which had by then metastasized. Surgery, then the only potentially curative treatment, was thus futile, and Hammerstein was told that he was expected to survive for merely another six months. Although his medical team admitted that the cancer had advanced beyond any hope of recovery, Hammerstein underwent radiation treatment, causing serious side-effects and great discomfort. His son, Kunrat, ordered that the therapy be discontinued after being informed that the treatment was purely palliative.