Leiomyosarcomas are a group of heterogeneous malignant tumours, which
originate in the smooth muscle mesenchyme and most often arise within the uterus,
soft tissues and gastrointestinal tract. Primary pulmonary leiomyosarcoma (PPL)
of the lung is extremely rare and accounts for less than 0.5% of all malignant
lung neoplasms 1.


Within the lung, PPL may originate from the smooth muscle cells of the
parenchyma, bronchial walls or pulmonary arteries and is classified according
to the site of origin 4. The intrapulmonary type is the most common type 5.

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The disease typically affects middle-aged adults, with a 2.5:1 male to
female predominance 6. Several risk factors have been linked to the development of PPL and
include radiotherapy, chemotherapeutic agents comprising of cyclophosphamide,
melphalan and nitrosuoreas as well as exposure to many occupational and
environmental agents including arsenic and herbicides 6.


Many patients with PPL, present with symptoms similar to other commonly
encountered bronchogenic neoplasms and include persistent cough, dyspnoea,
wheeze and haemoptysis alongside constitutional symptoms such as weight loss,
anorexia and malaise. Alternatively, patients can remain asymptomatic or
present as an incidental finding upon chest radiography, as was the case with
our patient.


Radiologically, the features of a PPL are often non-specific, and such
lesions typically occur in the lung peripheries as smooth, solitary
well-defined nodules or masses 3. As such, in order to differentiate a PPL
from a primary bronchogenic tumour an excisional biopsy is required with
careful histological examination and immunohistological staining. A diagnosis
of PPL should only be considered when there is no evidence of an occult primary
lesion elsewhere. In women, it is essential to exclude a concurrent uterine
leiomyosarcoma 2.


Pulmonary leiomyosarcomas demonstrate a wide spectrum of differentiation
and histologically are grossly characterised with a firm grey or white surface
4. Microscopically, malignant spindle cells are observed with slender cigar-shaped
nuclei arranged in interweaving fascicles 8. Low grade tumours are characterised by low mitotic rates and absence
of cellular atypia, necrosis and haemorrhage, whereas high-grade tumours have
marked cellular atypia, high mitotic rates with significant haemorrhage and
necrosis present 7.


Immunohistochemistry plays an essential role in differentiating PPL from
primary bronchogenic tumours alongside identifying the source of smooth muscle
and usually stain positive for actin, smooth muscle actin, desmin, vimentin and
negative for carcinoembryonic antigens, cytokeratin, neuroendocrine filaments,
S100 proteins and leukocyte common antigens 4, 6.


Due to the rarity of the disease, the treatment of PPL has not yet been
standardised. Current treatment modalities include surgical resection,
chemotherapy and radiotherapy. For small solitary well-differentiated tumours,
if amenable, complete surgical resection is considered curative. For larger
tumours, pre-operative radiotherapy may be indicated to decrease tumour size
prior to attempting surgical resection 6. In those, not amenable to surgical resection, then palliative
chemotherapy and radiotherapy remains the modality of choice. Despite this, the
prognosis remains poor with 5-year survival approaching only 35% 9.

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