Devita, Hellman, and Rosenberg's Cancer

LWBK1006-19 LWW-Govindan-Review December 7, 2011 21:24

Chapter 19•Neoplasms of the Mediastinum 223

limited utility for this indication. Posteroanterior (PA) and lateral chest

radiographs can define the general location, size and density of a medi-

astinal mass. Intravenous contrast-enhanced CT scan is the best imag-

ing modality for accurately defining whether the lesion is solid or cystic,

detecting fat and calcium, and determining the relationship of the mass

to surrounding structures. PET scan is useful for assessing mediastinal

lymphoma, but its role in the evaluation of other mediastinal masses con-

tinues to be evaluated.

Answer 19.4. The answer is A.

This woman has undergone complete resection of a noninvasive, low-

grade thymoma. Several histologic classification schemes and staging sys-

tems have been developed for thymic neoplasms. The WHO histologic

classification is most commonly used and includes both thymomas (types

A, AB, B1, and B2) and thymic carcinomas (types B3 and C) with vary-

ing degrees of pathologic atypia and aggressiveness. The most commonly

used staging system was derived by Masaoka: stage I, no microscopic

capsular invasion (noninvasive); stage II, microscopic capsular invasion

or gross invasion into perithymic fat; stage III, gross invasion into adjacent

organs; stage IVa, pleural or pericardial dissemination; and stage IVb, lym-

phogenous or hematogenous metastases. Complete resection of Masaoka

stage I low-grade thymoma is associated with 5- and 10-year survival

rates of 90% to 100% and 70% to 80%, respectively. Neither adjuvant

radiotherapy nor chemotherapy has been shown to benefit patients who

have undergone complete resection of Masaoka stage I, or noninvasive,

thymoma.

Answer 19.5. The answer is B.

This middle-aged man presents with anemia and a mediastinal mass that

is found to be a microscopically invasive, low-grade thymoma. The pres-

ence of capsular invasion is an adverse prognostic factor for patients with

completely resected thymoma, leading to a classification of Masaoka stage

II. Studies have suggested a survival advantage for adjuvant radiotherapy

after complete resection in patients with invasion into the capsule (stage II)

or adjacent organs (stage III). The role of adjuvant chemotherapy in such

patients remains unclear. Pure red cell aplasia occurs in 5% of patients

with thymoma and is believed to be caused by autoimmune dysregulation.

Conversely, 30% to 50% of patients with pure red cell aplasia have an

associated thymoma. Bone marrow examination shows marked reduction

or absence of erythroid precursors. Approximately 30% of patients also

have a reduction in megakaryocytes or leukocyte precursors. Thymec-

tomy induces remission of pure red cell aplasia in only 40% of patients.

Answer 19.6. The answer is D.

Many paraneoplastic syndromes are associated with thymoma, including

autoimmune disorders (polymyositis, systemic lupus erythematosus, Sjo-

gren’s syndrome, Hashimoto’s thyroiditis, and scleroderma), endocrine

disorders (Addison’s disease, hypothyroidism, and panhypopituitarism),