Ann Thorac Surg 1996;61:1525-1526
© 1996 The Society of Thoracic Surgeons
Case Report
Squamous Cell Carcinoma of the Lung: An Unusual Metastasis to Pectoralis Muscle
Peter P. McKeown, FRACS,
Patricia Conant, ARNP,
Lewis E. Auerbach, MD
Division of Cardiothoracic Surgery, University of South Florida, Tampa, Florida
Accepted for publication November 24, 1995.
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Abstract
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A 44-year-old man with clinical T2 N0 M0 squamous cell carcinoma of the lung presented 4 weeks after left pneumonectomy with a single metastasis to his right pectoralis major muscle. Three years after excision and chemotherapy he remains in remission. Muscle metastasis of carcinoma is an infrequent occurrence. Further investigation into the incidence and treatment is warranted.
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Introduction
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A 44-year-old man with a 75 pack-year smoking history presented with chest pain and shortness of breath. A 7.5 x 5-cm left infrahilar lung mass and small bilateral pleural effusions were present on roentgenogram. His medical history was significant for myocardial infarction, hypercholesterolemia, and a recent 6.75-kg weight loss. Mediastinal lymph nodes measured less than 1 cm on chest computed tomography. A metastatic evaluation including abdominal computed tomography, bone scan, and thoracentesis of pleural fluid was negative. Bronchoscopy brushings revealed squamous cell carcinoma. Intraoperative bronchoscopy showed external compression of the basilar segments of the left lower lobe, with no intrinsic lesions.
After clinical staging (stage 1, T2 N0 M0), plans for operative resection were made. Intraoperative intrathoracic nodal sampling found the aortopulmonary node and inferior pulmonary ligament node to be free of tumor. A left pneumonectomy was done. Pathologic examination confirmed poorly differentiated squamous cell carcinoma (Fig 1
). The tumor focally infiltrated the pulmonary artery, producing distal obstruction and thrombosis, and extended to the peribronchial lymph nodes, but the surgical margins were free of tumor (surgical stage II, T2 N1 M0). The patient had an uneventful recovery and was discharged on postoperative day 5. Radiation therapy was initiated 3 weeks after discharge.
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Fig 1. . Histologic appearance of original tumor: moderately differentiated squamous cell carcinoma of the left lung.
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Ten days later, after receiving 6 treatments (total of 1,080 cGy), he complained of a painful 3.2 x 3.0-cm mobile mass in the upper outer quadrant of the right breast. An excisional biopsy found the mass located at the lateral edge of the pectoralis major muscle to be metastatic squamous cell carcinoma (Fig 2). There was no further evidence of metastatic disease. A regimen of chemotherapy (cisplatin and VP16) was completed. A 3-year follow-up including computed tomography of head, chest, and abdomen as well as bone scans has revealed no evidence of tumor recurrence.
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Fig 2. . Pathologic appearance of metastatic squamous cell carcinoma to the right pectoralis muscle. Note the more pleomorphic appearance.
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Comment
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More than 157,000 new cases and 142,000 deaths per year in the United States are attributed to lung cancer, which has a 5-year survival of only 50% in patients who undergo resection. The 5-year survival in stage IV is only 8% [1]. Approximately 60% of patients with cancer have microscopic or clinically evident metastasis at the time of primary tumor treatment [2]. The complex mechanisms of metastases are not totally understood and involve an intricate and complicated series of tumor-host interactions. Liotta and Stetler-Stevenson [2] summarize the steps as (1) the metastatic tumor cell leaves the primary tumor, (2) enters circulation, (3) survives circulation, (4) stops at distant vascular bed, (5) invades the distant organ site, and (6) multiplies. Other factors of angiogenesis and host immunologic defenses influence the development, survival, and spread of metastatic disease. It is thought that less than 0.01% of circulating tumor cells initiate metastatic colonies [2]. The site of metastasis is not predictable, but may be related to the first capillary bed the metastatic tumor contacts or predilection of the distant organ for that tumor type either by preferential growth, specific adherence to the endothelial surface, or chemotaxic attractors.
Lung cancer has been known to metastasize to every organ system. Intrathoracic sites by local spread include mediastinal lymph nodes, pleura, diaphragm, chest wall, and pericardium. The most common extrathoracic sites are the adrenal glands, bone, kidney, and brain [3]. Squamous cell carcinoma frequently recurs locally, whereas adenocarcinoma metastasizes distally, most often to the brain. In those patients with squamous cell carcinoma, distal recurrences arise within 1 year in 73% of cases, with 87% appearing within 2 years. Metastatic lung cancer has only a 7.5% five-year survival [4].
Skeletal muscle metastases are rare (0.8% to 16% incidence in autopsy series) [5], and the reason is not well elucidated. The effect of lactic acid on tumor cell production [6], influence of variable and turbulent blood flow, ß-adrenergic stimulation, tissue oxygen levels, and host immune responses may provide a protective mechanism to skeletal muscle from tumor metastases [3]. Weiss [7], in a murine study, found that the survival of tumor cells injected into muscle was lowest in electrically stimulated muscle as compared with denervated muscle or noncontractile muscle. This suggests a mechanical inhibition in skeletal muscle preventing metastatic cell survival.
This case is unusual in several aspects. There was a high initial index of suspicion that this tumor was not resectable because of the clinical presentation of pleuritic chest wall pain and pleural effusion coupled with the large size of the tumor. Presence of pleural effusion does not always deem the patient inoperable, as tumor cells may not be present in the pleural fluid. There was no evidence of mediastinal adenopathy (all nodes were <1 cm on computed tomographic scan). A mediastinoscopy would not have been inappropriate, but the decision was made to proceed with the more aggressive intrathoracic evaluation, probably influenced by the patient's young age.
Intraoperatively intrathoracic lymph nodes at stations 5 and 9 were free of tumor. Pathologically the tumor focally infiltrated the pulmonary artery producing distal obstruction and thrombosis, which could indicate the mechanism of tumor spread. However, the metastatic focus developed on the opposite side of the primary tumor in the pectoralis muscle. Metastasis to skeletal muscle may be primarily hematogenous spread rather than via the lymphatic channels. In this case there was no lymph node involvement but there was positive infiltration into the vasculature. The development of metastases advanced his staging to stage IV with the likelihood of widespread metastatic disease and poor prognosis. Surprisingly, after an incomplete course of radiation therapy and a full course of chemotherapy, this patient remains disease free at 3 years. Most case reports of muscle metastasis report death within 1 year. Although trials with postoperative radiation and chemotherapy are ongoing, it seems prudent to have aggressively treated this patient who has obtained to date a better than expected outcome.
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Footnotes
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Address reprint requests to Dr McKeown, 4 Columbia Dr, Suite 730, Tampa, FL 33606.
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References
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- Baines MS. Surgical treatment of lung cancer. Chest 1991;100:826–37.[Free Full Text]
- Liotta LA, Stetler-Stevenson WG. Principles of molecular cell biology of cancer and cancer metastasis. In: DiVita VT, Hillman S, Rosenberg SA, eds. Cancer principles and practice of oncology. Philadelphia: Lippincott, 1993:134–49.
- Sridhar KS, Rao RK, Kunhardt B. Skeletal muscle metastases from lung cancer. Cancer 1987;59:1530–4.[Medline]
- Patterson GA. Lung cancer staging. Chest 1991;100:520–2.[Free Full Text]
- Sudo A, Ogihara Y, Shiokawa Y, Fujinami S, Sekiguchi S. Intramuscular metastasis of carcinoma. Clin Orthop Rel Res 1993;296:213–7.
- Seely S. Possible reasons for the high resistance of muscle to cancer. Med Hypoth 1980;6:133–7.[Medline]
- Weiss L. Biochemical destruction of cancer cells in skeletal muscle: a rate regulator for hematogenous metastasis. Clin Exp Metastasis 1989;7:483–91.[Medline]
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