DR. THELMA DUNN CLASSIFIED THE "SPONTANEOUS" MAMMARY TUMORS OF MICE IN 1957. HER
CLASSIFICATION IS STILL USEFUL TODAY. MOST OF THE TUMORS THAT SHE DESCRIBED CAME
FROM MuMTV INFECTED MICE. THE TWO MOST COMMON TUMORS ARE  TYPE A (LEFT) AND THE
TYPE B (RIGHT). THE TYPE A IS AN ACINAR TUMOR. THE TYPE B HAS MORE SOLID CORDS.