Radiation Oncology: A Question-Based Review


Robert C. Susil and Deborah A. Frassica

image Background

Chondrosarcoma accounts for what % of primary bone tumors?

Chondrosarcoma accounts for ~30% of primary bone tumors (behind osteosarcoma and multiple myeloma).

Are chondrosarcomas typically high- or low-grade lesions?

Most chondrosarcomas (80%) are low- to intermediate-grade tumors with relatively low metastatic potential.

What 2 precursor lesions may give rise to chondrosarcoma?

Osteochondroma (a cartilage-capped bony projection arising on the external surface of a bone) or enchondroma (a common, benign cartilaginous tumor that develops in the medulla of bone) may undergo malignant transformation to form chondrosarcoma.

What is the predominant age range for chondrosarcoma?

Most chondrosarcomas present in middle-aged to older pts.

What are the most common locations for chondrosarcomas?

Most chondrosarcomas (~75%) arise in the proximal femur, pelvis, or proximal humerus.

What are 3 common characteristics of pain associated with chondrosarcoma?

Pain associated with chondrosarcoma is typically insidious, progressive, and worse at night.

Chondrosarcomas of the skull base typically arise from what structures?

While chondrosarcomas of the skull base may arise from the clivus, most originate laterally from the spheno-occipital junction or less commonly from the spheno-ethmoid complex.

What is the typical pattern of spread for chondrosarcoma of the skull base?

Chondrosarcomas of the skull base are locally aggressive and may expand, destroying bone and compressing adjacent tissues.

What other tumor may often be mistaken for chondrosarcoma at the skull base? How can they be distinguished histologically?

Chordoma (particularly the chondroid variant) may appear similar to chondrosarcoma. Unlike chordomas, chondrosarcomas do not express cytokeratin or epithelial membrane antigen.

image Workup/Staging

What are 3 imaging tests commonly ordered for the workup of a possible chondrosarcoma?

Plain radiographs, MRI, and CT are commonly ordered for the workup of a possible chondrosarcoma. CT is best for examining tumor matrix mineralization, while MRI is best for assessing marrow and soft tissue involvement. In addition (especially for pts >40 yrs of age), CT C/A/P and other appropriate tests are often performed during the workup (to evaluate for possible metastatic Dz from an undiagnosed primary).

What is the characteristic plain film appearance of chondrosarcoma?

Although chondrosarcoma has a variable plain radiograph appearance, mineralization of chondroid matrix may produce a punctate or ring-and-arc pattern of calcification.

What 2 subspecialty referrals/workups should be performed prior to Tx of skull base chondrosarcoma?

Baseline neuro-ophthalmology and endocrinology workup is indicated for skull base chondrosarcoma.

What is the most common site for metastatic chondrosarcoma?

Although most chondrosarcomas have low metastatic potential, the lung is the most common site of metastatic Dz.

What are the AJCC 7th edition (2009) TNM stage categories for bone tumors?

1.     T1: ≤8 cm

2.     T2: >8 cm

3.     T3: discontinuous tumors in primary site

4.     N0: no regional LN mets

5.     N1: regional LN mets

6.     M0: no DMs

7.     M1a: DMs to lung

8.     M1b: DMs to nonpulmonary sites

What is the AJCC stage grouping for bone tumors?

1.     Stage Ia: T1N0, low grade

2.     Stage Ib: T2-3N0, low grade

3.     Stage IIa: T1N0, high grade

4.     Stage IIb: T2N0, high grade

5.     Stage III: T3N0, high grade

6.     Stage IVa: M1a

7.     Stage IVb: N1 or M1b

How is chondrosarcoma definitively diagnosed?

Chondrosarcoma is diagnosed by percutaneous core-needle Bx (which should be performed at the treating institution).

image Treatment/Prognosis

What type of surgical resection is typically recommended for chondrosarcoma?

WLE (i.e., removal of tumor and a cuff of normal tissue) is typically recommended for definitive surgical Tx of chondrosarcoma. For low-grade chondrosarcoma confined to the bone, some surgeons attempt to minimize morbidity by performing marginal excision (i.e., intralesional curettage) → phenolization/cryotherapy, then cementing/bone grafting (though this may cause increased risk of LR, it may be acceptable given the lesion's low metastatic potential).

When is RT recommended for chondrosarcoma? What are typical doses?

RT is typically recommended for unresectable chondrosarcoma or following margin + resection of recurrent or high-grade lesions. Doses >65 Gy are commonly recommended.

What is the recommended definitive Tx for skull base chondrosarcoma?

Surgical resection/debulking is recommended for skull base chondrosarcoma.

Why is PORT often recommended for skull base chondrosarcoma?

B/c gross total resection is often morbid for skull base chondrosarcoma (tumor resection is often piecemeal, and there may be adherence to critical structures), PORT is frequently recommended due to +margins or gross residual Dz.

What adj RT doses are necessary for control of skull base chondrosarcoma? What delivery methods are recommended?

Adj RT doses >65 Gy are needed for control of skull base chondrosarcoma. IMRT or proton therapy may be required to deliver this dose while respecting normal tissue tolerances.

When treated with surgical resection and adj RT, what control rates can be expected for skull base chondrosarcoma?

When treated with surgical resection and adj RT (to doses >65 Gy), control rates >90% can be expected for skull base chondrosarcoma (better than chordoma). (Rosenberg AE et al., Am J Surg Pathol 1999)

In general, is chemo recommended for chondrosarcoma?

No. Chemo is not generally recommended for chondrosarcoma (except for the dedifferentiated and mesenchymal subtypes, which according to NCCN category 2B recommendations can be treated as osteosarcoma and Ewing sarcoma, respectively).

What is a reasonable follow-up schedule for low- and high-grade chondrosarcoma?

According to the NCCN, a reasonable follow-up schedule for chondrosarcoma includes exam, local imaging, and chest imaging q6–12mos for 2 yrs, then annually. For high-grade lesions, recommendations include exam, local imaging, and chest imaging q3–6mos for 5 yrs, then annually for at least 10 yrs (as late recurrences may be seen).