PPB is mainly distinct from classic adult-type pulmonary
blastoma by the absence of malignant epithelial
elements [
6]. In pediatric patients the lesion is a true dysembryonic
neoplasm of thoracopulmonary mesenchyma,
without malignant epithelial cells. Pulmonary blastoma
with carcinomatous elements has only been described in
adults [
2]. Engagement of parietal pleura and diaphragm
can often be observed in type II and III, which have poorer
prognoses [
7]. Type II is similar to Wilms tumor morphologically
and therefore, it is sometimes incorrectly called
“extra-renal Wilms tumor” [
8]. Three pathologic types
based on gross and microscopic features have been defined
in the following manner: type I is a purely cystic
lesion that may be mistaken clinically and pathologically
for a congenital lung cyst; type II is a cystic and solid
lesion with areas of thickening and/or nodularity with or
without a relationship to the cysts; and type III is a purely
solid tumor consisting of friable, gelatinous to mucoid,
lobulated tissue often accompanied by hemorrhage and
necrosis [
3]. In immunohistochemical studies; the most
common findings were vimentin positivity and S-100 protein
positivity in cartilagenous foci positivity and desmin
positivity in areas with rhabdomyoblastic differentiation.
The only typical characteristic of tumor is vimentin positivity
[
9]. In our patient, pathological evaluation of tumor
was compatible with type II PPB. Cytogenetic studies of
childhood cases, chromosome anomalies of trisomy 8 and
2 karyotypic abnormality has been detected [
5,
10]. But
in our adult case, interestingly karyotypic abnormalities
such as trisomies 8 and 2 were not demonstrated.
Although surgery can yield positive results in type I
lesions, surgical success is rather more limited in type II
and III [1]. The most important prognostic factor is the total excision of the mass with clear margins. Postoperative
radiotherapy is recommended in cases with incomplete
resections [11]. Cyclophosphamide, doxorubicin, ifosfamide,
etoposide, vincristine are commonly used agents
in the treatment of PPB. The most common combination
is vincristine, dactinomycin, cyclophosphamide (VAC)
regimen. This treatment should be reserved for sarcomatous
lesions in particular [12]. Our patient received a total
of 6 cycles of IE/VAC regimen postoperatively. Toxicities
of the regimen were consisted of Grade 3/4 leukopenia in
two cycles with one febrile neutropenic episode.
Although metastases may not be present at diagnosis
in these patients, brain, liver and bone metastases can develop
in addition to local recurrence at the follow-up [13].
Recurrence and distant metastases, most commonly in the
central nervous system, can be observed in approximately
half of the patients [12]. The poor prognostic factors of
the disease are origin of cystic pulmonary disease, tumor size exceeding 5 cm, and mediastinal and/or pleural invasion.
Priest et al. [7] suggested that 2 years and 5 years
survivals were 62% and 42% respectively, despite aggressive
treatment in type II and III PPB. Our case has been
followed for thirty-sixth months without local recurrence
and metastases.
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