Standard Treatment Options

1. Surgical resection: Complete resection of a well-encapsulated, noninvasive thymoma is usually curative, with a risk of local recurrence of less than 2%. In patients with myasthenia gravis, operative mortality can be minimized with close attention to respiratory support when planning surgical treatment.

2. Radiation therapy is not indicated following complete resection of a well-encapsulated thymoma. Radiation therapy should be considered, however, in rare cases when a noninvasive thymoma is incompletely resected, and when the patient is a poor surgical risk.

Operable:

1. En bloc surgical resection if possible. In patients with myasthenia gravis, operative mortality can be minimized with close attention to respiratory support when planning surgical treatment.

2. Following surgical resection, radiation therapy is generally recommended whether or not the surgical resection has been complete, especially for stage III and stage IVa patients. Retrospective clinical studies show improved local control and survival with the addition of postoperative radiation therapy.

Inoperable (stages III and IV with vena caval obstruction, pleural involvement, pericardial implants, etc.):

3. Radiation therapy: In patients who have residual macroscopic tumor following biopsy or attempted resection, radiation therapy has been reported to achieve local control in 60% to 90% of cases. Because of an increased risk of radiation-induced injury, doses greater than 60 Gy should be avoided. Overall 5-year survival rates of approximately 50% are reported for patients with unresectable stage III tumors.It is uncertain whether patients who undergo tumor debulking have a better prognosis than those who undergo biopsy only.

1. Chemotherapy: Only a few phase II clinical studies have evaluated the role of chemotherapy in adequate numbers of patients. Combination chemotherapy has been reported to produce both complete and partial remissions; however, some of the complete remissions have been pathologically confirmed at subsequent surgery. In a series of 30 patients with stage IV or locally progressive recurrent tumor following radiation therapy, the PAC regimen (cisplatin, doxorubicin, cyclophosphamide) achieved a 50% response rate, including 3 complete responses. The median duration of response was 12 months, and 5-year survival was 32%.In another series, the ADOC regimen (doxorubicin, cisplatin, vincristine, cyclophosphamide) produced a 92% response rate (34 of 37 patients), including complete responses in 43% of patients. A study of combined chemotherapy with cisplatin and etoposide produced responses in 9 out of 16 patients treated, with a median response duration of 3.4 years and a median survival of 4.3 years.[9] In yet another study, 9 of 28 patients with invasive thymoma or thymic carcinoma who received 4 cycles of etoposide, ifosfamide, and cisplatin at 3-week intervals had partial responses. The median duration of response was 11.9 months (range, <1-26 months), and the median overall survival was 31.6 months. The 1-year and 2-year survival rates were 89% and 70%, respectively. Other combination chemotherapy regimens remain under evaluation. It remains uncertain whether combination chemotherapy regimens are more effective than single agents; no prospective comparisons have been conducted.

Transient partial responses have been reported with single-agent doxorubicin, maytansine, cisplatin, ifosfamide, and corticosteroids. It is important to remember, however, that corticosteroids and many chemotherapeutic agents are lympholytic; shrinkage of thymic tumors with substantial lymphoid cell infiltration may reflect shrinkage of the nonmalignant components of the tumors rather than the malignant epithelial components.

A retrospective analysis of 17 patients treated with cisplatin alone or in combination with prednisone revealed an overall response rate of 64%. Cisplatin alone (50 mg/m 2 every 21 days), however, was associated with a partial response rate of only 10% (2 of 20 patients) in a phase II study.

Treatment with single-agent ifosfamide was associated with 5 complete responses and 1 partial response in 13 patients with advanced thymoma in another prospective study.

2. Neoadjuvant chemotherapy followed by resection: A few studies have reported on the use of chemotherapy followed by surgery with or without radiation therapy for patients with clinically advanced disease.One series of 16 patients with stages III or IVa disease were treated with initial ADOC chemotherapy. All patients achieved a clinical response to chemotherapy. Eleven patients had residual histologic tumor and received postoperative radiation therapy. The median survival of the entire group was 66 months. Another similar study of 12 patients reported 100% survival and 73% disease-free survival at 7 years.Additional clinical studies are needed to confirm the value of preoperative chemotherapy before it can be recommended for routine use in this disease.

3. Combined chemotherapy and radiation therapy for unresectable tumors. An intergroup study of patients with unresectable disease who received cisplatin, doxorubicin, and cyclophosphamide followed by thoracic radiation reported a 5-year survival rate of 52%.

Standard treatment options (in order of decreasing effectiveness):

1. Repeat surgical resection, particularly for local recurrences and, in some cases, pleural and pericardial implants. Postoperative radiation therapy has been used for patients with incomplete resections and has been employed in selected patients following complete resection of recurrent thymoma.
2. Radiation therapy (when possible, based on previous treatment).
3. Corticosteroids in unresectable tumors that have not responded to radiation therapy.

1. Chemotherapy: Only a few phase II clinical studies have evaluated the role of chemotherapy. Because of the rarity of these cancers, all series of patients have been relatively small and reflect weak evidence. Combination chemotherapy, however, has been reported to produce complete and partial remissions; some of the complete remissions have been pathologically confirmed at subsequent surgery. In a series of 30 patients with stage IV or locally progressive recurrent tumor following radiation therapy, the PAC regimen (cisplatin, doxorubicin, cyclophosphamide) achieved a 50% response rate, including 3 complete responses. The median duration of response was 12 months, and 5-year survival was 32%.In another study, the ADOC regimen (doxorubicin, cisplatin, vincristine, cyclophosphamide) produced a 92% response rate (34 of 37 patients), including complete responses in 43% of patients.One study of combined chemotherapy with cisplatin and etoposide produced responses in 9 out of 16 patients treated, with a median response duration of 3.4 years and a median survival of 4.3 years.[4]Nine of 28 patients with invasive thymoma or thymic carcinoma who received 4 cycles of etoposide, ifosfamide, and cisplatin at 3-week intervals had partial responses.[5] The median duration of response was 11.9 months (range, <1-26 months), and the median overall survival was 31.6 months. The 1-year and 2-year survival rates were 89% and 70%, respectively.

It remains uncertain whether combination chemotherapy regimens are more effective than single agents; no randomized comparisons have been conducted. A partial response rate of only 10% (2 of 20 patients) was observed in a phase II study of cisplatin alone (50 mg/m 2 every 21 days). A retrospective analysis of 17 patients treated with cisplatin with or without prednisone over a 10-year period, however, revealed an overall response rate of 64%. Five complete responses and 1 partial response were observed in 13 patients with advanced thymoma in a prospective study of single-agent ifosfamide. Transient partial responses to corticosteroids have also been noted. It is important to remember, however, that corticosteroids and many chemotherapeutic agents are lympholytic; shrinkage of thymic tumors with substantial lymphoid cell infiltration may reflect shrinkage of the nonmalignant components of the tumors rather than the malignant epithelial components.

Antineoplastic agents — Combination chemotherapy using cisplatin is reported to have a response rate of 70-80%. Doxorubicin, vincristine, and cyclophosphamide have been used in combination chemotherapy.

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