Lactose and casein content of nonpuerperal breast secretion.

Twenty-seven patients with nonpuerperal breast secretion were evaluated for the presence of casein and lactose in the secretions. Only two of seven patients with brownish or greenish secretions were positive for both lactose and casein although an additional six patients were positive for casein alone. Two patients with clear breast secretions were positive for both casein and lactose. However, 16 of 17 patients with milky or white secretions were positive for both casein and lactose. Although casein and lactose are more likely to be present in white breast secretions, other types of breast secretions may also contain these constituents.