Pulmonary diffusion of breast cancer is frequent in those patients who have died of the disease and in those survivors who have not been cured after removal of the breast and X-ray treatment in the advanced states of the disease. When the metastases are identified, they are almost always multiple and bilateral. The appearance of a solitary, late, pulmonary coin lesion (metachrone), in someone with breast cancer certainly suggests a pulmonary metastase, but in fact, it is more likely to be a second cancer than a metastase, that is, a primary bronchopulmonary cancer. The presence of a solitary pulmonary coin lesion in someone who has or who has had breast cancer, presents therefore certain particular problems. After having controlled by xerotomography that there is no pulmonary diffusion in either lung, that there is no invasion of other tissues or organs, and after having controlled locally around the breast cancer, then it is imperative to remove the lesion without delay since it is certainly malignant and most probably a second cancer, that is, a primary bronchopulmonary cancer, an adenocarcinome, detected at an asymptomatic stage. The prognosis of a broncho-pulmonary adenocarcinome depends on the precocity of its removal.