Metastatic carcinoma from any site to skeletal muscle is extremely rare. Willis reviewed 500 consecutive autopsies on patients with malignancy to determine the routes of metastasis: 27 patients had known primary lung tumors, and none were found to have metastasized to skeletal muscle.1 Rarely, other malignant tumors including those arising from the thyroid;1 squamous cell lesions of the head and neck;1 male breast, pancreas, and stomach;2 kidneys;3,4 colon;5,6 squamous cell of lung;7 and mixed squamous cell and adenocarcinoma of lung8 have been reported to metastasize to skeletal muscles. In 1983, Steinbaum first described a metastatic adenocarcinoma of the lung to the thigh musculature, defined by computed tomography (CT).9 We report the second case of metastatic adenocarcinoma to muscle from a primary malignant lung lesion.
A 67-year-old man presented with a 4-month history of an enlarging tender mass in the medial aspect of his distal left thigh. He denied any general symptoms of fever, weight loss, anorexia, or weakness, and had no respiratory complaints of cough, hemoptysis, or chest pain. Medical history included the recent onset of "Parkinson's disease" diagnosed 5 months previously by a neurologist. He had a history of smoking 75 packs of cigarettes per year. Physical examination revealed a tender and mobile mass, measuring 5 cm by 6 cm and palpable within the vastus medialis, at the junction of the middle and distal thirds of the femur. The mass was not appreciably warm or pustular, nor was a bruit noted on auscultation. The mass moved with the quadriceps muscle and did not limit the knee from full flexion or extension. No adenopathy was observed, and the distal neurovascular examination was unremarkable.
Admission chest radiographs showed no active disease. Serum electrolytes, BUN, alkaline phosphatase, complete blood count, routine urinalysis, and ECG were all within normal limits. Plain radiographs did not show the soft tissue mass or any underlying bony involvement. Technetium bone scan demonstrated only a slight increase in uptake in the right temporoparietal region.
An open biopsy was performed through a longitudinal incision, and the frozen section demonstrated a poorly differentiated malignant spindle cell neoplasm. A wide excision was subsequently performed, and gross examination revealed a well defined mass with a pseudocapsule in the vastus medialis muscle. Permanent histologic sections demonstrated a poorly differentiated metastatic adenocarcinoma.
Additional diagnostic evaluation in search of the primary malignancy included an abdominal ultrasound, which was unremarkable, and CT scan of the chest and head. The primary lesion was identified on CT in the left upper lobe as a small nodular density extending to the pleural surface (Fig 1). A brain metastasis was also demonstrated in the left parietal area. The patient was treated with palliative radiation therapy to the pulmonary and brain lesions and was able to ambulate without difficulty with the knee immobilized. This case report was prepared 12 months after the surgical resection.
Gross examination revealed a 4.5 cm by 3.5 cm by 3.4 cm firm yellow-tan tissue mass with focal areas of hemorrhage and fibrosis. Surrounding muscle showed areas of fibrosis as well. Histologic examination revealed the tumor to be comprised of poorly differentiated, bizarrely shaped enlarged cells with large nuclei and prominent nucleoli. Abundant foamy eosinophilic cytoplasm was present, which on special staining contained globules of Alcian Blue positive, PAS positive, diastase-resistant material consistent with mucin, confirming the tumor to be an adenocarcinoma. Epithelial membrane antigen immunoperoxidase was positive, confirming the epithelial nature of the tumor. Acinar arrangement of tumor cells was also focally present (Fig 2).
Fig 1: Computed tomographic section through the upper lung fields demonstrating the primary lesion.
Fig 2: Histologic sections demonstrating the occasionally present focal areas of well differentiated, acinar-like formation of tumor cells associated with this metastatic adenocarcinoma. (3-A: hematoxylin and eosin, X200)
Despite the rich blood supply of skeletal muscle, primary tumor metastases to this tissue are rare; as noted by Willis in 1967: 'Tn view of the large aggregated blood supply to die entire musculature of the body, this paucity of metastatic tumors indicates the unsuitability of muscular tissue as a soil for the growth of arrested tumor emboli."10 Nevertheless, Pearson2 found in his review of 930 routine muscle biopsies in 110 necropsies that 14 muscles from six individuals had metastatic lesions. Three primary lesions were lymphomas and three were carcinomas, one each from a male breast, Vater 's ampulla, and the stomach . 2 Thirty-eight of Pearson's cases harbored malignancy at the time of death. It appears metastases to skeletal muscle from malignant lesions probably occur more frequently than commonly believed and may involve multiple muscles when they do occur. In Willis' review of 27 autopsies performed on patients with primary lung tumors, metastases were present in many organs and tissues including the liver, adrenal gland, brain, lung, kidney, myocardium, thyroid, pancreas, ovary, spleen, prostate, skin, intestinal mucosa, gallbladder, and pituitary, but there were none to skeletal muscle. In many cases, according to Wilson, the primary growth in pulmonary carcinoma "is symptomless, or nearly so, and it is the metastases which cause the first symptoms and dominate the clinical picture. ",0 Such was the circumstance in this case.
When a muscle metastasis is the presenting sign of a malignancy, the diagnostic work up for the lesion is dictated by the histology. Treatment of the nonsolitary metastatic carcinoma to muscle should be palliative. Pain or neurovascular compromise is an indication for surgical incision. If the mass represents a solitary metastasis and curative treatment of the primary lesion is contemplated, then wide resection of the mass may be appropriate, especially if an effective systemic chemotherapeutic agent is also available.
This is the second report in the English literature of metastasis to skeletal muscle from adenocarcinoma of the lung, and as in the previous case,9 the lesion presented as a mass in the quadriceps musculature. In contrast to the prior case, however, the preoperative chest roentgenograph did not reveal the primary lesion.
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2 . Pearson CM . Incidence and type of pathologic alterations observed in muscle in a routine autopsy survey. Neurology. 1959;9:757-766.
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6. Stulc JP. Petrelli NJ, Herrera L, et al. Isolated metachronous metastases to soft tissue of the buttock from the colonic adenocarcinoma. Dis Colon Rectum. 1985;28:117-121.
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8. Sarma DP. Kovac A, Soccorro N. Metastatic carcinoma of the skeletal muscle. South Med J. 1981;74:484-485.
9. Steinbaum S, Liss A. Tafrashi M. et al. CT findings in metastatic adenocarcinoma of the skeletal muscle. J Comput Assist Tomogr. 1983;7:545-546.
10. Willis RA. The spread of tumors in ihe human body, ed 3. London. Butterworths. 1973, pp 160-165, 282.