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Page 4 of 15 Pacheco et al. J Cancer Metastasis Treat 2020;6:49 I http://dx.doi.org/10.20517/2394-4722.2020.85

chondrocytes within the cartilaginous cap that retain one or both functional copies of EXT genes [9,13] . The
proliferative advantage and clonal outgrowth are likely driven by loss of cell cycle regulators CDKN2A and
TP53 [9,13,14] .

Diagnostic ancillary techniques
Immunohistochemical or molecular testing are not relevant for diagnosis.

Main differential diagnosis
Osteochondroma develops in skeletally immature patients during stature growth. Peak incidence is in
[1]
the first and second decades of life . As opposed to secondary peripheral chondrosarcomas, the great
majority of cases of osteochondromas occur in the growth plate area in the juxta-epiphyseal region of long
tubular bones and less frequently involve flat bones. The most objective parameters to raise suspicion of a
secondary peripheral atypical cartilaginous tumor/secondary peripheral chondrosarcoma grade 1 arising
in an osteochondroma is the presence in the latter, of a cartilaginous cap greater than 2 cm (measured
perpendicularly to the osteocartilaginous interphase). Nevertheless, this feature is in and of itself not
enough to make a diagnosis of secondary peripheral chondrosarcoma in the absence of other signs of
malignancy, such soft tissue invasion, as a very small percentage of osteochondromas may exhibits a
cartilaginous cap greater than 2 cm [2,15] . Microscopic features can greatly overlap, thus a multidisciplinary
approach to diagnosis is mandatory.

Periosteal chondrosarcoma lies directly over the cortex of the host bone and does not present
corticomedullary continuity of the tumor with the bone of origin. A peripheral layer of metaplastic bone (i.e.,
[16]
pseudo-cortex) is present in nearly 50% of periosteal chondrosarcomas .
Periosteal osteosarcoma contains osteoid-producing primitive mesenchymal cells between the cartilage
lobules, which are absent in secondary peripheral chondrosarcoma. Central chondrosarcoma is separated
from secondary peripheral chondrosarcoma by its location in the medullary cavity. The former is
molecularly characterized by IDH mutations, which are absent in secondary peripheral chondrosarcoma .
[17]

Treatment and prognosis
The treatment is surgery with wide margins, and will depend on the severity of symptoms, the size of
the lesion, and its location [18,19] . Amputation is necessary when the neoplasm is otherwise inoperable.
Radiotherapy and chemotherapy are not effective. Local recurrences can occur and are related to
incomplete excision. Prognosis after treatment is excellent and metastasis is very rare.

Periosteal chondrosarcoma
Definition and clinical features
Periosteal chondrosarcoma is a low grade malignant cartilaginous neoplasm of the bone surface that, by
[2]
definition, invades the underlying cortex and/or measures more than 5 cm . It is approximately three times
less frequent than periosteal chondroma [1,20] and represents 2.5% of all chondrosarcomas.

[1]
It occurs in adults, predominantly in males, with the peak incidence in the fourth decade . It typically
involves the metaphysis of long tubular bones, the distal femur being the most frequent location, followed
by the proximal humerus.

Imaging
Radiographic findings of periosteal chondrosarcoma include a round, lobulated mass on the surface of
bone with chondroid matrix mineralization in the form of “popcorn” opacities and sometimes metaplastic
ossification. Occasionally, the neoplasm can exhibit the same radiopacity as soft tissues. The underlying