Primary Lung Tumors

An 8 YO MC Chihuahua was presented to his referring veterinarian for previously scheduled thoracic radiographs to assess heart size due to a recently auscultated heart murmur.  The radiographs showed a pulmonary mass in the left caudal lung lobe and he was referred to the oncology service for further evaluation and treatment.

The owners reported that he had a good appetite and normal energy level.

On physical exam, he had a grade 3/6 left systolic murmur and no clinical signs of the mass were noted.

Radiologist review of the radiographs showed mild cardiomegaly and a single, well-defined 1.1 x 1.3 cm soft tissue opacity within the peri-hilar region of the left caudal lung lobe.  No evidence of metastasis was noted.

Complete Blood Count and Chemistry Panel were unremarkable and an abdominal ultrasound was performed which was also unremarkable.  Based on the peri-hilar location on radiographs, a thoracic CT scan was performed to more appropriately assess the location and determine if the mass was resectable.  The CT demonstrated a 1.3 x 1.8 x 1.6cm mass in the left caudal lung lobe at the level of the main-stem bronchus.  No thoracic lymphadenopathy or pulmonary metastasis was noted.  CT is considered the standard of care for primary lung tumors in order to fully stage the patient and for surgical planning.

Capture1 Capture2Image 1:  This is a CT image of the patient preoperatively.  The mass is identified with the red asterisk (*) and the bronchus is identified with the yellow (+) sign.  As visible in the CT images, the mass is located immediately adjacent to the bronchus.

The most common neoplastic etiology of a primary lung mass is a pulmonary adenocarcinoma with other differentials including squamous cell carcinoma, sarcoma, and adenoma.  With any primary lung mass, surgical resection is the initial step in treatment and due to the unremarkable CT scan, surgery was recommended in this case.  He was taken to surgery, and a left caudal lung lobectomy was performed via a left lateral incision.  A tan mass was noted to extend to the proximal extent of the lung tissue in the left caudal lobe and resection was performed by ligation of the bronchus, pulmonary artery, and vein.  In most cases, lung lobe resection can be performed with a thoracoabdominal (TA) stapler leaving a small margin of lung tissue but in this case, this was not possible because all of the proximal pulmonary tissue was grossly effaced by the mass.  The tracheobronchial lymph nodes were not enlarged and due to the small size of the patient, lymph node biopsies could not be safely obtained.  Recovery anesthesia was uneventful and he was discharged 48 hours later.  At the time of this report, the patient is still alive, 27 months post-operatively.

Histopathology of the mass revealed a well-differentiated pulmonary carcinoma (low grade) with a 0.1cm of bronchial margin with incomplete margins.

The prognosis with pulmonary carcinoma is variable and depends on several factors including the presence of metastasis, tumor size, presence of clinical signs, and the histopathologic analysis.  The best prognosis is in cases of tumors that are not associated with clinical signs, have no evidence of metastasis, have a size of less than 5 cm and have no evidence of lymphadenopathy.  (Ogilvie, Mehlhaff)  Histologically, the best prognosis is noted with a well-differentiated pulmonary adenocarcinoma, in which a mean survival time of 19 months is noted. (Mehlhaff).  Squamous cell carcinoma in the same study had a mean survival time of 8 months.

Proposed prognostic factors for primary lung tumors include:

  1. Size (< 5 is good)
  2. Metastasis (poor)
  3. Malignant effusion (poor)
  4. Tumor adhered to chest wall (poor)
  5. Squamous cell carcinoma (poor)
  6. Undifferentiated tumors (poor)
  7. Tumor in the periphery (good) vs central (poor)
  8. Clinical signs at presentation (poor)
  9. High-grade tumor (poor) vs low grade (good)

In cases of complete resection with criteria for a good prognosis mentioned above, chemotherapy is not typically recommended.  In this case, because the margins were determined to be incomplete, metronomic chemotherapy was offered but declined by the owners.  The use of chemotherapy for primary lungs tumors is unknown at this point as the paucity of information exists in the literature regarding its efficacy. Generally, chemotherapy is reserved for the following scenarios:

  1. Post surgery: patient with poor indicators and deemed at risk of recurrence or spread
  2. Nonresectable or metastatic tumors

Chemotherapy protocols vary between oncologists and no true standard of care exists, however, Carboplatin, Doxorubicin, Vinorelbine all have efficacy. Recently, the use of novel antiangiogenic strategies such as tyrosine kinase inhibitors and metronomic chemotherapy is being evaluated in these case, however, data is lacking.

Submitted by:  Brian Bretz, DVM, DACVS

HOPE Veterinary Specialists, Malvern, PA

References:

  1. Ogilvie GK, Weigel RM, Haschek WM et al: Prognostic factors for tumor remission and survival in dogs after surgery for primary lung tumor: 76 cases (1975-1985). JAVMA 195: 109-112, 1989
  1. http://www.ncbi.nlm.nih.gov/pubmed/?term=Prognostic+factors+for+tumor+remission+and+survival+in+dogs+after+surgery+for+primary+lung+tumor
  1. Mehlhaff CJ, Leifer CE, Patnaik AK et al: Surgical treatment of primary pulmonary neoplasia in 15 dogs. JAAHA 20:799-803, 1984.
  1. http://www.ncbi.nlm.nih.gov/pubmed/?term=mehlhaff+Surgical+treatment+of+primary+pulmonary+neoplasia+in+15+dogs
  1. Withrow SJ, Vail DM: Withrow and MacEwen’s Small Animal Clinical Oncology. St. Louis. Saunders Elsevier, 2007. 4th Print.
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