Primary lung tumors are uncommon in dogs accounting for about 1% of all tumors. A much more common finding are metastatic cancers in the lungs of dogs. Primary lung tumors are most often seen in older dogs (10-12 years old), but there are no gender or breed predispositions. They tend to be indolent, slow growing tumors and so often clinical signs do not develop until the cancer has spread, or the tumor has become severe enough to cause pleural effusion or other related problems that will make breathing more difficult. These tumors may also cause an abnormal proliferation of bone in the distal limbs, called hypertrophic osteopathy, which is painful and may result in lameness. A diagnosis is often made with chest radiographs (x-rays), and may even be made while looking at the chest for other reasons given the indolent nature of this disease. Advanced imaging such as a CT scan may be recommended because this imaging modality is much more sensitive than standard x-rays for looking for metastases to other parts of the lung. The abdomen should also be examined to look for distant spread. Biopsies may be taken either by fine needle aspiration if the tumor is located in the peripheral lung, or surgically. Treatment involves surgery to remove the tumor if possible. Chemotherapy is only used if metastases are detected, or if surgery is not an option. The prognosis for primary lung tumors in dogs is highly variable and depends on multiple factors such as tumor size, location, type, grade, and whether or not there is evidence of metastasis. A solitary, small tumor (<5 cm) located at the periphery of the lung carries the best prognosis, and with surgery alone median survival time is reported to be around 20 months. A high grade tumor with spread to local lymph nodes or other lung lobes carries a much poorer prognosis.
Primary lung cancer is much more common in people and is currently the number one cause of cancer related death in people. Although smoking is associated with most lung cancer in people, it most likely is not the predominant cause of primary lung tumors in dogs. That being said, second hand smoke has been associated with development of tumors in pet animals, and can contribute to development of primary lung tumors especially in brachycephalic breeds (short nosed dogs).