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merkel cells are primarily located in the basal layer of the epidermis and concentrated in touch - sensitive areas of the skin .
their most noticeable ultrastructural characteristics are the dense - core secretory granules accumulated near the nerve fibre junction , which may contribute to its indefinite neuroendocrine function .
merkel cell carcinoma ( mcc ) was first described by toker in 1972 as trabecular carcinoma of the skin .
85% of all mccs appear on sun - exposed areas with the head and neck region most frequently affected , accounting for 3547% of these cases .
the prognosis is poor , with a 5-year survival rate of around 60% , owing to the common involvement of regional lymph nodes ( 1045% ) at initial presentation , of which 5075% of patients develop regional lymph node metastases at some time .
distant metastases commonly affects 50% of patients with common sites being the lymph nodes , liver , bone , brain , lung and skin . orouke and bell first described complete spontaneous regression ( csr ) of mcc in 1986 .
this present study presents a case of complete spontaneous regression of mcc with an immunohistochemistry study of the region in which the tumour was located .
an 86-year - old female patient presented with a violaceous lump on the left side of the nose measuring 25    25  mm .
an incisional biopsy was performed and histology showed a dense infiltrate of small tumour cells with hyperchromatic nuclei and little cytoplasm ( fig .
1 ) . immunohistochemistry confirmed the diagnosis of mcc , with positive staining for cytokeratin 20 ( ck20 ) ( fig .
3 ) , synaptophysin and negative staining for cytokeratin 5/6 t , ttf1 and melana .
the patient attended for an excision 8 weeks after her initial biopsy and showed no presence of lump prior to excision ( fig .
histology of the excised specimen showed severely sun - damaged skin with mild epidermal atrophy .
there was a patchy chronic inflammatory cell infiltrate with focal fibrosis and foreign body giant cell reaction with no evidence of any residual mcc .
immunohistochemistry demonstrated a mixture of both t and b cells with positive staining for cd4 , cd3 , cd5 , and cd8 with cd4 slightly more than cd20 and cd79a .
spontaneous regression among all neoplastic diseases has been estimated to be 1 case per 60,000 to 100,000 neoplasms .
complete spontaneous regression ( csr ) of mcc is rare and predicted to be 0.0013% . to date , 15 cases of complete mcc regression following incisional biopsy have been reported ( table 1 ) , along with 7 cases of regression occurring after local or regional recurrence of the carcinoma ( table 2 ) . in the group of mccs with primary csr
in contrast , none of the cases of mccs with csr after local recurrence or metastasis were primarily located on the cheek . in both groups of patients
the majority were female ( 15 cases ) and the mean age was 79 years old .
our patient presented the typical characteristics of patients with primary csr of mcc i.e. female sex , elderly and regression after incisional biopsy .
the histopathologic study of the biopsy following csr in our patient demonstrated results similar to other reports .
other studies of both primary and secondary mcc demonstrated infiltration by cd4 + , cd8 + and cd3 + t lymphocytes and foamy macrophages .
the mechanism of csr remains unclear , however , along with our findings , it suggests that t - cell - mediated immunity plays an important role in tumour regression .
this could be attributed to the initial incisional biopsy of mcc ( 15 cases ) , which may have triggered tumour regression via stimulation of the immune system .
in addition , the majority of patients were elderly with poor health status and various co - morbidities , which may suggest other unknown mechanisms , could be involved .
in summary , we report one patient with csr of mcc . to the best of our knowledge ,
the findings are in concordance with many other studies most notably an incisional biopsy before regression and an infiltrate of t cells after regression .
although , this is only a proposed mechanism it certainly is an area that requires further research with the possibility of developing immune modulating therapy in treating such cancers .
written informed consent was obtained from the patient for publication of this case report and accompanying images .
calver pang  data collection , data analysis , writing ; deepika sharma  histopathological and immunohistochemistry studies including figures ; thangasamy sankar 
study design , patient details.key learning pointsmerkel cell carcinoma is a rare disease with a high metastatic rate and poor prognosis.spontaneous regression of merkel cell carcinoma is an extremely rare event.in this case report , regression occurred following incisional biopsy.biopsy showed mainly t cells suggesting immunity plays an important role in tumour regression which may be attributed to the incision which triggered an immune response.mechanism of regression is still unclear but research into immune modulating therapy may help in managing such cancers .
merkel cell carcinoma is a rare disease with a high metastatic rate and poor prognosis.spontaneous regression of merkel cell carcinoma is an extremely rare event.in this case report , regression occurred following incisional biopsy.biopsy showed mainly t cells suggesting immunity plays an important role in tumour regression which may be attributed to the incision which triggered an immune response.mechanism of regression is still unclear but research into immune modulating therapy may help in managing such cancers .
merkel cell carcinoma is a rare disease with a high metastatic rate and poor prognosis .
spontaneous regression of merkel cell carcinoma is an extremely rare event . in this case report
biopsy showed mainly t cells suggesting immunity plays an important role in tumour regression which may be attributed to the incision which triggered an immune response .
mechanism of regression is still unclear but research into immune modulating therapy may help in managing such cancers .
introductionmerkel cell carcinoma ( mcc ) is a rare and highly aggressive primary cutaneous neuroendocrine carcinoma , most often occurring in the elderly . 
 recurrence is frequent and in 40% of cases regional and distant metastases develop . despite this , 
 there have been reports of spontaneous regression . 
 we report the first case of mcc with primary complete spontaneous regression of the nose in an 86-year - old woman following an incisional biopsy.presentation of casean 86-year - old woman presented with a violaceous lump on the left side of the nose measuring 25    25  mm . 
 incisional biopsy of the lesion showed mcc and immunohistochemistry confirmed diagnosis . following an 8-week period the lesion completely disappeared and 
 histology did not show any residual mcc but immunohistochemistry demonstrated a mixture of t and b cells.discussioncomplete spontaneous regression ( csr ) is rare . 
 the literature documents 22 similar cases of csr of mcc . from this case report and previous literature 
 the most likely reason for regression is a t - cell mediated immune response.conclusionto the best of our knowledge , this is the first described case of mcc with primary csr of the nose . 
 exact mechanism of regression remains unclear . 
 further research is needed in identifying pathway of immune response and possible immunotherapy as a cure .