Perhaps the men are cancer survivors in the story. The white characters could be memories or hallucinations. After going through the trauma of cancer, the men are haunted by white - looking apparitions. These could be the memories of the pain, the fear of recurrence, or the actual hallucinations caused by the strong medications they took during treatment. The horror lies in the fact that these white characters keep coming back, making it difficult for the men to fully move on from their cancer experience.