In this context, the term soft tissue refers to tissues that connect, support, or surround other structures and organs of the body. Soft tissue includes muscles, tendons (bands of fiber that connect muscles to bones), fibrous tissues, fat, blood vessels, nerves, and synovial tissues (tissues around joints).

There are many different kinds of soft tissue sarcomas. They are grouped together because they share certain microscopic characteristics, produce similar symptoms, and are generally treated in similar ways. (Bone tumors, also known as osteosarcomas, are also called sarcomas, but are in a separate category because they have different clinical and microscopic characteristics and are treated differently.)

Sarcomas can invade surrounding tissue and can metastasize (spread) to other organs of the body, forming secondary tumors. The cells of secondary tumors are similar to those of the primary (original) cancer. Secondary tumors are referred to as "metastatic soft tissue sarcoma" because they are part of the same cancer and are not a new disease.

Some tumors of the soft tissue are benign (noncancerous). These tumors do not spread and are rarely life-threatening. However, benign tumors can crowd nearby organs and cause symptoms or interfere with normal body functions.

What are the possible causes of soft tissue sarcomas?

Scientists do not fully understand why some people develop sarcomas while the vast majority do not. However, by identifying common characteristics in groups with unusually high occurrence rates, researchers have been able to single out some factors that may play a role in causing soft tissue sarcomas.

Studies suggest that workers who are exposed to phenoxyacetic acid in herbicides and chlorophenols in wood preservatives may have an increased risk of developing soft tissue sarcomas. An unusual percentage of patients with a rare blood vessel tumor, angiosarcoma of the liver, have been exposed to vinyl chloride in their work. This substance is used in the manufacture of certain plastics.

In the early 1900s, when scientists were just discovering the potential uses of radiation to treat disease, little was known about safe dosage levels and precise methods of delivery. At that time, radiation was used to treat a variety of noncancerous medical problems, including enlargement of the tonsils, adenoids, and thymus gland. Later, researchers found that high doses of radiation caused soft tissue sarcomas in some patients. Because of this risk, radiation treatment for cancer is now planned to ensure that the maximum dosage of radiation is delivered to diseased tissue while surrounding healthy tissue is protected as much as possible.

Researchers believe that a retrovirus plays an indirect role in the development of Kaposi's sarcoma, a rare cancer of the cells that line blood vessels in the skin and mucus membranes. Kaposi's sarcoma often occurs in patients with AIDS (acquired immune deficiency syndrome). AIDS-related Kaposi's sarcoma, however, has different characteristics and is treated differently than typical soft tissue sarcomas.

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Pulmonary Cysts as the Sole Metastatic Manifestation of Soft Tissue Sarcoma - )
From CHEST, 7/1/99 by Seiki Hasegawa

Case Report and Consideration of the Pathogenesis

A 29-year-old woman with an unusual form of pulmonary metastasis from epithelioid sarcoma of the right forearm is presented. Since she manifested left pneumothorax due to metastatic pulmonary cyst 7 years ago, the only metastatic manifestation has been the presence of bilateral multiple thin-walled pulmonary cysts; no other types of pulmonary lesions, such as nodules, cavitary lesions with thick or irregular walls, or extrapulmonary metastases, have been found. Pathologic studies revealed metastatic proliferation of sarcoma cells in the wall of the pulmonary cysts and infiltration of malignant cells inside the microscopic cavitary metastases surrounded by normal lung parenchyma. (CHEST 1999; 116:263-265)

Key words: cystic metastasis; pneumothorax; pulmonary cyst; pulmonary metastasis; sarcoma

Cystic pulmonary lesions caused by metastasis of soft tissue sarcoma are rare. When accompanied by multiple pulmonary nodules, such lesions can be easily identified as possible metastases from an unidentified primary tumor. However, when a pulmonary cyst is not accompanied by pulmonary nodules or a noticeable primary lesion, it may not be readily identified as a pulmonary metastasis.

We describe a 7-year follow-up of a patient in whom spontaneous pneumothorax and multiple pulmonary cysts were the initial clinical manifestations of epithelioid sarcoma of the forearm. Detailed serial histologic studies revealed the possible mechanism by which the malignant cysts developed.

CASE REPORT

A 29-year-old Japanese woman was admitted to Nagahama City Hospital in June 1996 because of recurrent left pneumothorax. She had several episodes of pneumothorax in both lungs. She had undergone left thoracotomy in November 1991 and right thoracotomy in December 1993, and the histologic diagnosis of the resected lung tissue was pulmonary bulla with metaplasia of the lining cells in all instances.

Chest CT on admission revealed bilateral pulmonary thin-walled cysts measuring up to 2.0 cm in diameter. Results of physical and laboratory examinations were unremarkable, except for a tumor on the right forearm. The patient underwent partial resection of the left S10 segment, which contained several subpleural bullae. No other intrapulmonary or pleural lesions were found during surgery. Although pulmonary bulla with inflammatory reaction was the histologic diagnosis, pathologists could not rule out mesothelioma or other malignant diseases of the lung, because the lining cells of the cyst wall showed atypia.

After completion of the treatment for left pneumothorax, a detailed examination of the tumor on the right forearm was performed. The patient had noticed (1) slight but progressive disturbance in extension of the right middle and ring fingers since 1986 and (2) a small nodule on her right palm since 1991. Radiologic studies revealed a longitudinal mass located on the ulnar side of her distal forearm measuring 2 to 4 cm in diameter and 15 cm in length, and a small nodule on the medial-distal side of the right upper arm measuring 1 cm in diameter. A biopsy led to a pathologic diagnosis of epithelioid sarcoma of the right forearm and metastasis to the regional lymph nodes.

A detailed histologic reassessment of lung specimens obtained in 1991, 1993, and 1996 was made. pulmonary tissue was compared with the tissue removed from the forearm, and they were similar. Thus the cystic lesions in these specimens were diagnosed as metastases of epithelioid sarcoma. Systemic screening with CT and MRI was performed, but no other metastatic lesions were found. No abnormal uptake was observed by whole-body scintigraphy with [.sup.99m]Tc-methylene diphosphonate and gallium citrate Ga 67, and slight uptake was observed only in the right forearm tumor with thallous chloride T1 201.

The patient is currently well, her only symptom being motor disturbance in the right upper extremity. Her laboratory results show no abnormalities and there is no evidence of distant metastasis except to the lungs.

Radiologic Study

Multiple pulmonary cysts with thin and smooth walls in both lungs were observed by chest CT in June 1996 (Fig 1, top, A). Most of these lesions were intraparenchymal and a few were subpleural. Serial CT studies revealed that these cystic lesions appeared where only normal lung parenehyma had been seen in previous CT scans, and that they grew slowly (Fig 1, bottom, B). No nodules, cavitary lesions with thick or irregular walls, necrotic tissue in the cysts, pleural lesions, or enlarged lymph nodes were found throughout the follow-up period.

Pathologic Study

The macroscopic features of the cysts in the resected lung were consistent with those of pulmonary bullae. Light-microscopic studies were performed on formalin-fixed, paraffin-embedded, and hemotoxylin-eosin-stained samples. The walls of the cysts lacked lining epithelium and consisted of a dense proliferation of large spindle cells with eosinophilic cytoplasm (Fig 2). Nuclear atypism of the tumor cells was prominent, but no mitoses were observed. Both fresh and old hemorrhages, hemosiderin deposits, and partial calcification were seen in the cyst walls. There were several microscopic cavitary lesions surrounded by normal lung parenchyma, and the walls of the cavities were lined with sarcoma cells (Fig 3).

DISCUSSION

Pulmonary metastases of soft tissue sarcomas commonly take the form of solid nodules. However, only 14 eases, including the present ease, of cystic pulmonary metastases from soft tissue sarcomas have been reported. In four of these cases, thin-walled cysts were the only manifestation of pulmonary metastases. The eases involved the following patients: a 20-year-old woman with leiomyosarcoma of the uterus, a 19-year-old woman with leiomyosarcoma of the ankle, an 86-year-old man with angiosarcoma of the scalp, and the 29-year-old woman of the present study[1-10] (Table 1).

Table 1--Soft-Tissue Sarcoma Cases in Which Thin-Walled Cysts Were the Only Metastatic Manifestation in the Lung(*)

(*) None of the patients had received previous chemotherapy or radiation therapy. F = female; M = male.

There is confusion or overlapping concepts about excavating, cavitary, and cystic pulmonary metastatic tumors. Excavating pulmonary metastasis may be defined by the mechanism of its formation; it is initially a solid mass and its air-filled cavity is formed after discharge of the necrotic material inside. Therefore, such lesions usually have a thick and irregular wall and are seen with other lesions at various stages of excavation. A cystic pulmonary metastasis is a thin-walled, bulla-like lesion with or without accompanying

nodular lesions.

Three possible mechanisms for the development of malignant cysts have been described[9,11,12]: (1) excavation of a nodular tumor through discharge of the necrotic material inside, (2) infiltration of malignant cells into the walls of a preexisting benign pulmonary bulla, and (3) infiltration of malignant cells into the walls of air sacs formed by cystic distension of small airways through the ball-valve effect of the tumor. Involvement of the first mechanism in the present case was ruled out because no nodules or thick-walled cavitary lesions appeared during the 7-year follow-up period. The second mechanism was also unlikely, because the consistent increase in the number of pulmonary cysts could hardly be explained by a progressive emphysematous change in the lungs of this young, nonsmoking woman. The likelihood of the third mechanism is strengthened by the presence of microscopic cavitary metastases; these lesions are considered to be an early stage in the development of macroscopic thin-walled cysts. Thus we conclude that the pathogenesis of the metastatic cysts in the present ease may have involved the third mechanism.

REFERENCES

[1] Farrell JT. Pulmonary metastasis: pathologic, clinical, roentgenologic study based on 78 cases seen at necropsy. Radiology 1935; 24:444-451

[2] Lodmell EA, Capps SC. Spontaneous pneumothorax associated with metastatic sarcoma. Radiology 1949; 52:88-93

[3] Depierre R, Chomette G, Abelanet R, et al. Metastases pulmonaires diffuses seules manifestations d'un sarcome primitif de l'oreillette droite. Presse Med 1961; 69:159-160

[4] Laucius JF, Brodovsky HS, Howe CD. Spontaneous pneumothorax and pneumomediastinum as complications of sarcoma. J Thorac Cardiovasc Surg 1972; 64:467-471

[5] Wright FW. Spontaneous pneumothorax and pulmonary malignant disease; a syndrome sometimes associated with cavitating tumors: report of nine new cases, four with metastases and five with primary bronchial tumors. Clin Radiol 1976; 27:211-222

[6] Mehzad M. Leiomyosarcoma of the uterus presenting with pneumothorax. Br J Dis Chest 1977; 71:132-134

[7] Sarno RC, Carter BL. Bullous change by CT heralding metastatic sarcoma. Comput Radiol 1985; 9:115-120

[8] Lemarie E, Belin T, Lemaire B, et al. Metastases pulmonaires excavees, a parois fines, d'un sarcome du col uterin. Rev Pneumol Clin 1986; 42:153-156

[9] Traweek T, Rotter AJ, Swartz W, et al. Cystic pulmonary metastatic sarcoma. Cancer 1990; 65:1805-1811

[10] Angulo JC, Lopez JI, Flores N. Cavitation of lung metastases from bladder cancer: report of two cases. Tumori 1993; 79:141-143

[11] Anderson H J, Pierce JW. Carcinoma of bronchus presenting as thin-walled cysts. Thorax 1954; 91:100-105

[12] Dodd CD, Boyle JJ. Excavating pulmonary metastases. Am J Roentgenol Radium Ther Nucl Med 1961; 85:277-293

(*) From the Department of Thoracic Surgery (Drs. Hasegawa and Inui), the Department of Pulmonology (Dr. Kamakari), and the Department of Orthopedic Surgery (Drs. Kotoura and Suzuki), Nagahama City Hospital, Nagahama, Japan; and the Department of Pathology (Dr. Fukumoto), Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.

Manuscript received October 19, 1998; revision accepted January 7, 1999.

Correspondence to: Seiki Hasegawa, MD, Department of Thoracic Surgery, Kyoto University Hospital, 53 Shogoin, Kyoto 606-8397, Japan; e-mail: seikiha@kuhp.kyoto-u.ac.jp

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