Metastatic lung cancer. Light microscopy (LM) of a section through pulmonary tissue showing a metastatic melanoma. Lungs are the second most frequent site of malignant melanoma metastases after lymph nodes, but they are the most common initial site of systemic relapse. Lung metastases at presentation of primary tumor are rare (5%) but at autopsy are extremely common (70%-80%). Malignant melanoma is known for unpredictable behavior, sometimes with pulmonary involvement after a prolonged period of latency. Magnification: x80 when printed 10 centimetres wide.