A 15 year old male presented with a soft tissue mass on ...



California Tumor Tissue Registry’s

Case of the Month

, vol 8(2),

November, 2005

“A 15 y/o male with a lump on his arm”

A 15-year-old male presented with a soft tissue mass on his right upper arm. The excised nodule was solid, lobulated and measured 2.0 x 1.8 x 0.8 cm.

The tumor involved deep dermis and subcutaneous tissue, and displayed mostly a solid growth pattern. It was infiltrative into fat and focally encompassed vessels and nerves (Fig. 1). There were nests of small, rounded histiocyte-like cells associated with spindle-shaped fibroblastic-like cells (Figs. 2-4). The polygonal histiocyte-like cells had prominent nucleoli (Figs. 5, 2). Occasional multinucleated giant cells were also seen (Fig. 3, left top).

Diagnosis: Plexiform Fibrohistiocytic Tumor, Mixed Type

Barbara Semakula and Donald R. Chase, MD

Loma Linda University Medical Center, California, U.S.A.

First reported in 1988 by Enzinger and Zhang, plexiform fibrohistiocytic tumor (PFT) is a painless, uncommon tumor of low malignant potential. With only about 100 cases in the literature much information is still anecdotal (rather than statistical). The tumor mostly affects children, adolescents and young adults and has a mean age of occurrence of 14.6 years. There is a strong female predilection (6:1). The tumor is usually small (1-3 cm) and arises in soft tissue. It is indolent and many times takes months to years to attain significant size. The upper extremities are usually involved (63%), but the tumor may also occur in the lower (14%). The head/neck region has been involved in only one reported case.

Usually the tumors are non-encapsulated, poorly circumscribed and show an admixture of fibroblasts, mononuclear histiocyte-like cells and multinucleated osteoclast-like giant cells. Little or no cellular atypia is seen. Three fourths of the tumors display mitotic activity but only 14% have atypical forms.

The dominant cell type varies from tumor to tumor resulting in somewhat arbitrary separation into three variants. These variants are recognized for their diagnostic merits, not for predicting outcome.

• Fibrohistiocytic (36%),

• Fibroblastic (32%), and a

• Mixed Variant, a combination of the two (32%).

Fibrohistiocytic PFTs are composed of well-defined nodules of histiocyte-like cells with pale cytoplasm and round to oval, centrally-located nuclei having one or more small nucleoli. Also characteristic of this variant are multinucleated osteoclast-like giant cells with abundant eosinophilic cytoplasm and three or more round nuclei, each with a single prominent nucleolus. Although fascicular growth is seen, the predominant pattern is one of lobularity.

In the fibroblastic variant there is predominant growth in fascicles many of which are short and swirled, and interconnect to form plexiform (or “fingerprint-like”) configurations. The spindled cells have pale cytoplasm with slender, tapered nuclei with tiny nucleoli. The spindle cells are oval or elongated.

Mixed lesions contain features of both the fibrohistiocytic and fibroblastic variants and have evenly arranged plexiform fibrohistiocytic nodules mixing with fascicles of spindled fibroblasts.

Immunohistochemically the multinucleated giant cells and many of the mononuclear cells express CD 68, suggestive of true histiocytic differentiation. The cells, however, do not mark for other histiocyte markers such as HLA-DR, lysozyme, or L-2. The spindled cells express smooth muscle actin similar to myofibroblasts. They are negative for S-100 protein, keratin, desmin, and factor XIIIa. Ultrastructural studies have revealed features of histiocytes and myofibroblasts. Flow cytometry results has shown a diploid S-phase fraction from 0.93% to 7.22% and a G2M phase from 0.41% to 5.57%.

PFTs have been shown to be low grade malignancies which may recur locally or metastasize, especially when primary tumor control is incomplete. When metastatic, PFT may spread either via lymphatics to regional lymph nodes or via blood vessels to the lungs. In a 1999 retrospective study by Remstein et al, 22 cases of PFT were reviewed. Sixteen patients were alive with no evidence of disease (82%), 1 (6%) was alive with metastatic disease, 1 (6%) was alive with a stable pulmonary nodule of unknown nature, and 1 (6%) had died of disease three years after local recurrence and subsequent distant spread to lymph nodes and lungs. Two patients (12.5%) had local recurrence, 1 (6%) had regional lymph node metastasis, and 3 (19%) had pulmonary metastases.

References and Suggested Reading:

1. Enzinger F, Weiss S. Soft Tissue Tumors 3rd edition, 1995 Mosby - Year Book Inc. 343 - 349.

2. Mori O, Hashimoto T "Plexiform fibrohistocytic tumor" Eur J Dematol. 2004 Mar-Apr; 14 (2): 118-20.

3. Pfau M, Ruck P, Schaller HE "Plexiform fibrohistiocytic tumour - case report of a rare low-malignant tumour with frequent localisation at the upper limb" Handchir Mikrochir PlastChir. 2002 May; 34 (3): 201-4.

4. Remstein ED, Arndt CA, Nascimento AG. "Plexiform fibrohistiocytic tumor: clinicopathologic analysis of 22 cases." Am J Surg Pathol. 1999 Jun; 23 (6): 662-70.

5. Salamao DR, Nascimento AG, "Plexiform fibrohistiocytic tumor with systemic metastases: a case report" Am J Surg Pathol. 1997 Apr; 21 (4):469-76.

6. Segura LG, Harris J, Wang B, Rienzo A, Urken ML, Brandwein M. "Plexiform fibrohistiocytic tumor: a rare low-grade malignancy of children and young adults" Arch Otolaryngol Head Neck Surg. 2002 Aug;128 (8):966-70.

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