Merkel cell carcinoma of the thumb with squamous and leiomyosarcomatous differentiation

ARTICLE

Auteur(s) : Renato Covello¹, Stefano Licci², Angela Ferrari³, Luca Morelli⁴, Caterina Catricalà³

¹Department of Pathology, National Cancer Institute “Regina Elena”, Rome, Italy
²Department of Pathology, “Santo Spirito” Hospital, Lungotevere in Sassia, 100193 Rome, Italy
³Department of Dermatologic Oncology, Dermatologic Institute “Santa Maria and San Gallicano”, Rome, Italy
⁴Department of Pathology, “Santa Chiara” Hospital, Trento, Italy

A 69-year-old woman presented for a one year history of a skin lesion on her left thumb with rapid growth in recent months. She had no palpable lymphoadenopathy on clinical examination. The lesion appeared as a pink, ulcerated nodule, suspicious for squamous cell carcinoma.

Histologically, the lesion consisted of a nodular ulcerating neoplasia, deeply infiltrating into the dermis and subcutaneous fat, composed of small round-to-oval malignant cells with scant cytoplasm and a high mitotic rate, admixed with islands of squamous cell carcinoma and an undoubtedly malignant spindle cell tumour (figures 1ABC). There was also a squamous cell carcinoma in situ in the epidermidis close to the lesion (figure 1D). The small cell component represented about 60% of the lesion, the squamous cell component 30% and the spindle cell component 10%.

Immunohistochemistry showed that the small cell component was strongly positive for NSE and for CK (AE1/AE3) and CK20, with a paranuclear dot-like positivity (figure 1E), while CK7, TTF1, vimentin, s-100 protein, smooth muscle actin (SMA), desmin, caldesmon and HMB45 were all negative. The spindle cell malignant component showed a strong positivity for vimentin, desmin, SMA (figure 1F) and caldesmon, while all the other markers were negative. The squamous cell carcinoma component resulted positive only for CK (AE1/AE3).

On the basis of the immunomorphological findings, a diagnosis of MCC with squamous and leiomyosarcomatous differentiation was made. One month later, the patient developed an ipsilateral axillary lymphoadenopathy and a radical axillary lymph node dissection was performed.

Ten of the twenty lymph nodes examined showed metastatic disease with extranodal invasion. Unlike the primary neoplasm, only the Merkel cell component, with an identical morphological and immunohistochemical profile, was found in the metastasis. The patient underwent adjuvant chemotherapy and regional radiotherapy but, unfortunately, she died one year after the first diagnosis.

MCC is a rare, aggressive, neuroendocrine carcinoma of the skin, usually occurring in sun-damaged skin in the head and neck region of elderly people [1]. Toker, who first described this tumour in 1972, called it trabecular carcinoma and supposed an eccrine origin. Later, in 1978, with the ultrastructural demonstration of neurosecretory granules in the cytoplasm of the tumour cells, a neuroendocrine origin was postulated [2]. Recently, an epidermal origin of Merkel cell has been supported, due to the observation of an association between MCC and squamous cell carcinoma [3]. Interestingly, in these cases the clinical behaviour was highly aggressive, as in typical MCC. Since the risk factors for MCC and squamous cell carcinoma of the skin are overlapping, it can be supposed they represent collision tumours [4]. The intimate admixture of the different neoplastic cell types and the presence in some cases of transition cells with features of both Merkel cells and squamous cells suggest a common origin from the same stem cell [3]. Moreover, six cases of Merkel cell carcinoma with sarcomatous differentiation have been described [5], one of them with a leiomyosarcomatous component [6]. In our case, the primary lesion was represented by MCC with squamous and leiomyosarcomatous differentiation, but only the MCC component was present in the metastatic regional lymph nodes, unlike Hwang's case [5], in which the metastatic lymph nodes displayed both the MCC and sarcomatous components. A possible explanation could be that the MCC component was the prevalent one, representing about 60% of the whole lesion, while the leiomyosarcomatous part constituted only about 10% of the tumour. Furthermore, MCC is more prone to give rise to lymph node metastasis than squamous cell carcinoma, representing, in our case, about 30% of the neoplasia. This finding seems to suggest a possible role of the proportions of the different components in the primary lesion in predicting the metastasizing potential of the disease.

Acknowledgments

References

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