Giant solitary trichoepithelioma
from the Clinic for Plastic and Reconstructive Surgery, Copenhagen Department of Pathology, Hvidovre Hospital, University
of Copenhagen , Div. Of Dermatology, Department of Medicine, and Dept. of Pathology, Roskilde Hospital, Roskilde, Denmark
Jemec B, , Løvgreen Nielsen P, Jemec G B E, and E Balslev
Dermatology Online Journal 5(1):1
The giant solitary trichoepithelioma is a rare trichogenic tumor with potential for local recurrence. Only nine cases have been previously described in the literature, and one additional case without recurrence during the first 3.5 years of observation is presented stressing that the rate of recurrence is low.
The epidemiology and precise malignant potential of rare tumors is generally difficult to assess. The more common or the more lethal tumors are generally well described, either because they are available to regular population based studies, or because they are recognized and treated in specific centers making follow-up much easier. For the large number of rare tumors neither of these approaches is available, and knowledge therefore rests on compilation of individual cases.
A 48-year-old man was referred for excision of a large subcutaneous mass on the left shoulder. The tumor was growing slowly, but did not cause subjective symptoms. On inspection a subcutaneous tumor measuring 4 x 2 x 1,5 cm was found. This was clinically similar to a lipoma and there were no palpable regional lymph nodes.
The tumor was excised under local anesthetic. The tissue was sharply demarcated, solid in consistency, white in color and lobulated in nature. Histologically the tumor was found to be entirely subcutaneous, with a normal overlying epidermis, and was composed of lobules with anastomosing streaks of uniform basaloid cells which were without atypia; all surrounded by a fibromyxoid stroma.
|Figure 1||Figure 2|
Figure 2: The glandular nature of the GST
In several places the cells were congregated in immature hair cell structures and the tumor showed no evidence of malignancy. See Fig. 1. This was reported as a Giant Solitary Trichoepithelioma.No sign of recurrence was seen during the first 45 months of follow up.
|Figure 3||Figure 4|
Figure 4.: Nodular elements.
|Figure 5: Giant solitary Trichoepithelioma|
Giant Solitary Trichoepithelioma (GST) is an unusual neoplasm of the hair germ and nine cases only have previously been reported in the literature (Table 1). Recurrence has been described  but our knowledge of the clinical behavior of the tumor and recurrence rate is limited.
Because of the rarity of these hair germ tumors, classification is difficult and several schemes have been proposed. Hair germ tumors are heterogeneous biological manifestations of epithelial and mesenchymal interactions and have been classified according to the relative predominance of either component.[2, 3] Rosen proposed another classification whereby the tumors are divided unto categories depending on which part of the developing hair follicle they resemble. Ackerman also  classified the benign hair follicle tumors after the most prominent morphological part. Finding an overlap between tumors described for histopathological purposes, Wong et al (Wong 1993) proposed a simplified nomenclature whereby similar tumors were grouped under the term benign trichogenic tumors, thus avoiding this overlap due to excessively detailed description of few cases. The previous precise and detailed description of the tumors was also thought unnecessary by Schirren et al  especially as they believed the tumors described showed a continuum of subtle morphological changes with a great similarity. They proposed that all tumors with a follicular germinative cell are named Trichoblastoma. We have found in grouping all the above classifications that the GST is always described separately. Reports describing trichoblastomas have therefore been excluded from our survey.
The trichoepithelioma derives from the inferior segment of the follicle epithelium as a hamartoma.[3,4] Three clinical forms of trichoepithelioma are recognized [8,9]:
- a small solitary form
- a small multiple form which is inherited in an autosomal dominant fashion
- a rare giant solitary form
Histologically  all three forms of trichoepithelioma are similar but not identical. They all show a well demarcated tumor clearly differentiated as hair forming structures. Immature hair appears as keratinous cysts surrounded by basophilic cells in an adenoid pattern. In addition to the obvious clinical differences in size and number between the different types of trichoepithelioma, the subcutaneous tissue [1,9] and the presence of extensive fibromyxoid stroma  have been proposed as indicative of GST, See Figure 1.GST has been defined as a solitary trichoepithelioma with a diameter greater than 2 cm  Few cases of GST have been described (See table 1) making clinical data scarce.
Although GST has been described on the head, seven of the nine previously described cases have occurred on the lower body. The mean age of the published cases was 60 years with a range of 31-77 years, suggesting that the tumor may appear at any age, but shows a predilection for the older age group. The reported tumors have been growing for an average 25.4 years before excision and the M:F ration of the reported cases is 2:1. The majority of the GST have been subcutaneous, but pedunculated , ulcerated  and cystic  forms appear as well.
|110||58||M||8 (0)||20||R Thigh||None/?|
|311||53||M||6.5x4.5x3.0||3.5||R Thigh||None/9 mo|
|415||77||F||3.5x188.8.131.52||7||Natal cleft||None 18 mo.|
|515||71||M||5.0x3.5x2.5||many||Buttock||None/ 1 year|
|615||70||F||3.5x2.5x2.0||10||Natal cleft||None/ 6 mo|
|71||31||M||2 (0)||?||Scrotum||17 years|
|10||48||M||4.0x2.0x1.5||?||L Shoulder||None/ 3.5 y|
Table 1: Overview of the key clinical aspects of previously reported of GST.
Trichoepitheliomas in general are benign tumors, but in one of the only nine published cases of the giant solitary form recurrence after surgery has been described and an increased clinical awareness as well as follow up therefore seems indicated in this rare neoplasm.
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