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overall lung cancer is the most common cancer , in terms of both incidence as well as mortality .
metastasis to liver , adrenals , bones , brain , and kidney have been reported .
metastasis distal to knee and elbow are rare and even rarer is solitary metastasis to fibula . till date , in the literature only 10 cases of solitary fibular metastasis have been reported , out of which lung was the primary site of malignancy in only four cases .
the authors report a case of lung carcinoma undergoing chemotherapy that initially did not have any bony metastasis but presented with a painful swelling below the knee that turned out to be a solitary fibular metastasis on biopsy .
a 50-year - old male came to outpatient department of our tertiary care center with complaints of left sided chest pain for 2 months , hoarseness of voice for 1 month , and cough with hemoptysis .
there was history of chronic smoking . on examination , the patient was stable , nondyspnoeic with normal vitals .
a computed tomography ( ct ) scan of the chest was advised , which revealed a large , irregular , heterogeneous soft tissue density mass lesion in the left upper and lingular lobe of size ~6.3 cm  5.6 cm  11 cm ( ap  t  cc ) .
there were a few , well defined ground - glass nodules in bilateral lung fields suggestive of metastasis with left sided pleural effusion .
histopathological examination from left lung mass was suggestive of poorly differentiated squamous cell carcinoma of the lung . also , pleural fluid cytology examination was positive for malignancy .
contrast enhanced ct ( cect ) abdomen and bone scan done as a part of metastatic work up revealed no distant metastasis .
taxane- and cisplatin - based chemotherapy was started at three weekly interval . during the course of treatment , after receiving the third cycle of chemotherapy , the patient developed severe pain in the right knee and proximal leg . on examination ,
a fusiform swelling with ill - defined margins was noted on the anterolateral aspect of the right knee joint [ figure 1a ] .
it was ~3 cm  2.5 cm in size , hard , fixed , and tender .
later on , an x - ray of the knee joint was done that revealed an expansile lytic lesion of fibula [ figure 1b ] .
cect knee showed an ill - defined , expansile , destructive lesion on the posterolateral aspect of the head of fibula with a large , heterogeneously enhancing soft tissue component .
fnac from the lesion in the fibula was performed that showed malignant squamous cells with evidence of keratinization suggesting the possibility of metastasis [ figure 1c ] .
biopsy from the lesion confirmed metastatic squamous cell carcinoma to fibula [ figure 1d ] .
the patient was given palliative local radiotherapy 30 gray in 10 fractions for fibular metastasis .
after 15 days of palliative irradiation the patient was evaluated , there was partial reduction in the size of the lesion but he got complete relief of pain .
patient was planned for second line chemotherapy but unfortunately he did not return and was lost to follow - up . ( a ) clinical photograph of the swelling ( b ) x - ray of knee joint ( lateral view ) shows lytic expansile lesion of the head of fibula ( c ) fine needle aspiration cytology of the lesion shows clusters of malignant squamous cells ( triangle ) with evidence of keratinization ( solid arrow ) ( 100 ) with evidence of intracytoplasmic keratinization ( solid arrow , inset ) ( 400 ) ( d ) h and e stained section showing malignant squamous cells with hyperchromatic nuclei and dense eosinophilic cytoplasm ( arrow ) ( h and e 400 )
fibula as the site of solitary metastasis from any primary tumour is extremely rare . till date to the best of our knowledge , only 10 cases of solitary fibular metastasis have been reported . out of these 10 cases , in four cases the primary tumour was in lung as seen in our case .
four cases of gynaecological malignancies have been reported with solitary metastasis to fibula . and , one case of renal and gastric origin with solitary fibular metastasis has been reported . in these 10 cases
the youngest patient was 36 years old with primary cervical cancer , whereas the oldest patient , who had lung carcinoma , was 76 years old . among the 10 cases previously reported in literature
three patients with primary lung cancer and one patient with vaginal cancer had solitary metastasis to fibula at the time of presentation , whereas one patient of lung cancer as well as the patient with gastric cancer developed fibular metastasis 6 months after detection of primary tumor . a female patient with carcinoma cervix developed fibular metastasis 9 months after treatment . in patients with endometrial cancer and primary renal cell carcinoma
, fibular metastasis was detected 5 years after the initial presentation . in the present case ,
fibular metastasis was seen after 2 months from the initial diagnosis of primary lung cancer . in all these patients pain and swelling
this type of presentation at unusual sites , initially suspected as nonmalignant inflammatory conditions , as seen in our case leads to delay in diagnosing these findings .
although bone scan is generally accepted as the initial method of choice for bone metastasis assessment , it is not performed as a routine clinical practice in our setup unless otherwise it is clinically indicated . in this patient
, baseline bone scan was performed that was negative for bony metastasis . at the time of presentation of fibular disease ,
bone scan was not done as the clinical index of suspicion was more in favour of an infective or unrelated pathology , such as osteomyelitis .
moreover , there were no symptoms and signs suggestive of skeletal metastasis elsewhere in the patient .
the unique features of this case are the involvement of long bone ( fibula ) as the sole metastatic site with no clinical feature indicative of metastasis throughout the rest of the skeleton and presentation as an inflammatory swelling .
this case report gives insight that any new complaint or / and finding in the patient developing during treatment should be evaluated carefully with high index of suspicion for metastasis so that active intervention could be done timely .
solitary bone metastasis to fibula in patients of lung carcinoma is a rare entity , with only four cases reported in literature . 
 we , hereby , present a case of a 50 year - old - male who was given three cycles of chemotherapy for lung carcinoma with no distant metastasis but presented 2 months later with a fusiform , painful swelling around the knee that was clinically suspected to be inflammatory in nature but proved to be fibular metastasis on cytology . 
 there was no evidence of skeletal metastasis on initial bone scan . 
 he was given palliative radiotherapy for this with symptomatic relief .