metastasis to the oral cavity is a rare event and constitutes 1% of all oral cavity malignancies . oral cavity metastases are mostly observed in the jaws compared to the soft tissues , particularly in the posterior area of the mandible . clinically , early gingival metastases are polypoid or exophytic , highly vascularized , and resemble hyperplastic or reactive lesions such as pyogenic granuloma , giant cell granuloma , and peripheral fibroma . metastasis to the oral cavity is one of the complications of systemic cancer and usually develops in the end stage of a cancer lesion . oral cavity metastases are an increasingly critical cause of morbidity and mortality in cancer patients . thus , oral cavity metastasis presents a therapeutic challenge and is a physically debilitating event for the patient . early diagnosis and treatment of oral cavity metastasis dentists play a crucial role in the diagnosis and management of cancer patients , especially in those patients in whom oral metastasis is the first sign of undiscovered cancer in other parts of the body . the purpose of the present article was to review the characteristics of the oral soft tissues metastases to analyze all available information . a relevant english literature search in pubmed , scopus , and google scholar was performed . the keywords  oral cavity ,   soft tissue ,  and  metastasis  were searched in the title / abstract of publications limited to 1930 to 2015 . all variables such as age , gender , and primary and secondary tumor sites were analyzed . in some of reports , especially in case series , most of the variable assessments were incomplete . in general , there were 412 metastatic lesions that developed in the oral soft tissues . lung cancers mostly metastasized to the gingiva with 46 cases ( 11.1% ) , followed by the tonsil and tongue with 11 cases each ( 2.6% ) . majority of liver cancers metastasized to the gingiva in 26 cases ( 72.2% ) of all metastatic lesions from liver cancer . breast cancers also mostly metastasized to the gingiva in 20 cases ( 60.6% ) of all metastatic lesions from breast cancer . however , kidney cancers mostly metastasized to the tongue ( 19 cases of all metastatic lesions from kidney cancer ; 36.5% ) . most of the gingival metastases were detected in posterior areas . metastasis in edentulous cases was found in only 7 cases ( 1.7% ) . in 14 cases ( 3.4% ) , metastatic tumors were distributed equally in the right and left sides . in 19 cases ( 4.6% ) , metastatic tumors developed in the anterior region and in 11 cases ( 2.6% ) developed bilaterally . in 62 cases ( 15% ) , the metastatic lesion developed in the contralateral side of the primary tumor . in 69 cases ( 16.7% ) , the greater part of the histological examination yielded adenocarcinoma ( n = 93 ; 22.5% ) , followed by variants of renal carcinoma ( n = 54 ; 13.2% ) , hepatocellular carcinoma ( n = 41 ; 10% ) , and in lower numbers , malignant melanoma ( n = 21 ; 5% ) and squamous cell carcinoma ( n = 18 ; 4.4% ) . there were 5 cases of osteosarcoma , 4 cases of chondrosarcoma , and 3 cases of ewing 's sarcoma . most reported cases were from the united states of america with 63 cases ( 15.2% ) , followed by korea and spain with 45 ( 11% ) and 32 cases ( 7.8% ) , respectively . the results of the literature search of cases of oral soft tissue metastases are summarized in tables 1 and 2 . table 3 shows the comparison of the results of this review with those of the previous reviews . a summary of oral metastasis in men a summary of oral metastasis in women comparison of the results with those of previous reviews the incidence of metastasis is rising with the increase in the survival of cancer patients . at present , cancer patients live longer due to advances in cancer diagnosis and management . the majority of head and neck cancer cases are related to tobacco use and heavy alcohol consumption . other possible risk factors include viral infections , infection with candida species , and a number of bacterial species . the criteria for the diagnosis of a metastatic tumor are as follows;first , the primary tumor must be histologically verified . second , the metastatic tumor and primary tumor must be of the same histological type . finally , the possibility of direct local spread from the primary tumor must be excluded . metastasis to distant organs is not a random event , and is regulated by a site - specific process . for example , breast and prostate cancers usually metastasize to the jaw bones , however , lung carcinomas commonly metastasize to the oral soft tissues . there are a few reports of oral metastases from the tumors with high mortality rate such as pancreatic cancer probably due to patient 's death before the appearance of a metastatic lesion . in this review , there were only 2 cases of metastatic pancreatic cancer . in the cases of bone involvement , it is not clear whether the cancer cells directly metastasize to the gingiva , or a bone metastasis subsequently extends into the gingiva , or the patient had both gingival and bone metastases ; however , it is suggested that the cancers first metastasize to the gingiva , and then cancer cells invade to the underlying bone . in the current review , the involvement of both gingiva and bone was found in 69 cases . the gingiva is the most common site for metastasis ; inflammatory reaction such as gingivitis or periodontitis could be critical factors to facilitate metastasis . some degree of inflammation in the gingival tissue can be found in most people . in chronically inflamed gingiva , the role of inflammation in the attraction of metastatic cells has been suggested previously , and it might be the reason for a higher frequency of metastases in the attached gingiva . on the other hand , there are some reports of metastases to the post - extraction site , which indicate the role of local factors in the extraction or wound area that may attract circulating tumor cells . tooth extraction may serve as a promoting factor in metastasis as it creates a microenvironment rich in growth factors . it is suggested that tooth extraction site is a microenvironment rich with local growth factors which favor the growth of metastatic cells . the tongue is also a highly vascular organ , and hence , the high incidence of metastatic tumors can be explained . these findings are in agreement with the role of both inflammation and angiogenesis in cancer metastasis . according to a review by yoshitomi et al . the tongue is a frequent site for renal cell carcinoma metastasis and usually indicates a widespread disease . in the present series , there were 58 cases of metastasis from the kidney , and in 19 cases the tongue was the metastatic site . the second most common primary site metastasized to the tongue was the lung with 11 cases . some other studies revealed that the most common tumors metastases to the tonsil are malignant melanoma and small - cell bronchogenic carcinomas . for example , the majority of lung cancers metastasizing to the tonsils are of the small cell type , thus , adenocarcinomas rarely metastasize to the tonsil . however , this review indicated that most of the metastatic tumors to the tonsil were adenocarcinomas ( 14 cases ) , followed by malignant melanoma ( 11 cases ) , and there were only 2 small cell carcinomas metastasizing from the lung . providing an exact diagnosis is very challenging for a pathologist . if the history of a previous cancer exists , the histopathological findings of the metastatic lesion should be compared with those of the primary cancer . special staining such as immunohistochemistry can be helpful in identifying the nature of the primary tumor . in addition to the batson 's plexus , the other possible routes of oral metastasis include arterial , venous , and lymphatic circulations . however , in cases such as lung cancer , direct extension by aspiration , access to the pulmonary vein , and drain to the left side of the heart has been suggested . cancer cell clusters drain into the portal vein and then travel to the heart and finally deposit in the lungs . in cases of gastric cancer , stomach contents in addition , retrograde dissemination of the tumor to the tongue with involvement of regional lymph nodes is another possible route in the cases of tongue metastasis . as the palatine tonsils do not have afferent lymphatic vessels , the metastatic pathway is difficult to determine in palatal tonsil metastases . metastasis to the oral cavity mostly occurs in the advanced stage of the disease and indicates widespread disease . the prognosis and treatment depends on the site of primary tumor and degree of metastatic spread . the metastatic lesion should be treated by surgical resection , radiation , chemotherapy , or a combination of these methods . palliative treatment reduces the patient 's pain , size of tumor , and preserves oral function . the diagnosis of a metastatic lesion in the oral cavity is a challenge to the clinicians due to the lack of pathognomonic signs and symptoms . oral metastases usually occur in the advanced stages of cancers , and the interval between appearance and death is usually short . therefore , due to a high mortality rate , patients with oral lesions , particularly those with a history of a malignancy , deserve a careful diagnostic procedure . even with the diagnosis of a primary lesion , it is necessary to make a definite diagnosis of oral lesions for appropriate treatment . early detection of oral lesions is important in the case of being the first sign of a malignancy in other parts of the body .
the present review article analyzes the characteristics of metastases to the oral soft tissues from 1937 to 2015 . 
 an extensive literature search was performed . 
 all variables such as age , gender , and primary and secondary tumor sites were analyzed . 
 metastases to the major salivary glands were not included in this review . in general , there were 412 metastatic lesions developed in the oral soft tissues . 
 the male - to - female ratio was approximately 1.8:1 . 
 the mean age of the patients at diagnosis was 58 . 
 the lung was the most common primary site and the gingiva was the most common metastatic site . 
 the greater part of the histological examination yielded adenocarcinoma . 
 the diagnosis of a metastatic lesion in the oral cavity is a challenge to the clinicians due to the lack of pathognomonic signs and symptoms . 
 oral metastases usually occur in the advanced stages of cancers , and the interval between appearance and death is usually short . 
 the oral soft tissue metastasis can be easily recognized compared to the metastasis of jawbones . 
 early detection of oral lesions is important in the case of being the first sign of a malignancy in other parts of body .