This white blood cell was found in the bloodstream of a patient with malignant lymphoma.
The nucleus is a bit large for a normal lymphocyte, without a corresponding increase in cytoplasmic size as you'd expect in a reactive lymphocyte.
The groove in the nucleus corresponds to a stage in lymphocyte development in germinal centers. One should not see these cells in the circulation. This is cancer.
The ring on the red blood cell to the left is an air bubble trapped in the mounting medium.