Metastatic squamous cell carcinoma of the lung masquerading as a soft tissue tumor

Abstract

Carcinoma of lung can metastasize to any organ system; however, metastasis to skeletal muscles is extremely rare. A 63-year-old man, known case of pulmonary tuberculosis on treatment, presented with a painful swelling in his left leg. Examination revealed a 5.0 cm × 3.0 cm calf swelling, which on imaging was suggestive of a soft tissue tumor. Fine-needle aspiration cytology of the swelling revealed it to be squamous cell carcinoma. Further investigations revealed a mass in the left lower lobe of the lung. Biopsies from both the lung lesion and calf swelling confirmed the diagnosis of squamous cell carcinoma of lung with metastasis to the calf muscle. The case is being presented because of its unusual presentation and rarity.

Upfront skeletal muscle metastases from non-small cell lung carcinoma: Report of an extremely rare occurrence detected by 18F-fluorodeoxyglucose positron emission computed tomography scan

“…Although 18FDG-PET/CT can identify silent metastatic lesions, the definite diagnosis of origin is identified by HPR supported by IHC. [ 2 7 ] The most common differential diagnosis of SMM is STS and notwithstanding the various clinical criteria, HPR do differentiate between the two which becomes more relevant in case of silent metastases[ 7 ] as was seen in our case. Tissue biopsy from both primary lung lesion and SMM showed adenocarcinoma with IHC positivity for TTF-1 and SMM staining negative for desmin, a muscle-specific protein.…”

“…[ 4 ] Wittich in 1854 reported the first incidence of SMM, while Willis first reported SMM from lung. [ 5 ] NSCLC most commonly metastasizes through hematogenous route to distant organs such as brain (10%), bones (7%), liver (5%), and adrenal gland (3%), while SMM accounts for a mere 0.0%–0.8%,[ 2 ] which depicts the rarity of such occurrence. Most information regarding this rare phenomenon has been described in case reports and few case series with maximum 16 cases of lung SMM reported by Pop et al .…”

“…SMM occurs more commonly in males compared to females with smoking as the principal predisposing factor. [ 5 8 10 ] For SMM, pain is the most common symptom followed by palpable mass[ 2 3 4 5 6 7 8 9 10 ] whether SMM gets detected before or synchronously within 6 months or metachronously after 6 months of diagnosis of primary. [ 5 ] A painful mass has often been associated with SMM in contrast to STS,[ 8 ] while a silent SMM like our case has been scarcely reported.…”

“…Skeletal muscle metastases (SMM) from non-small cell lung carcinoma (NSCLC) though documented is extremely rare[ 1 ] with an incidence of 0.0%–0.8%. [ 2 ] Gastrointestinal and genitourinary tract malignancies are the most common primaries[ 3 ] with an overall incidence of 0.8%–1%. [ 4 ] SMM presents most commonly with pain or palpable mass,[ 4 5 ] but an asymptomatic lesion detected by 18F-fluorodeoxyglucose positron emission/computed tomography (18FDG-PET/CT) has been seldom reported.…”

“…18FDG-PET/CT scan is the imaging modality of choice for detecting SMM. [ 6 ] Histopathology (HPR) remains the gold standard of differentiation from soft-tissue sarcomas (STS)[ 2 7 ] and initiation of appropriate therapeutic modality, though no definitive measure does exist due to its rarity. [ 5 8 ]…”