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Correspondence |
-Smooth Muscle Actin Expression: A Mimic of Inflammatory Myofibroblastic Tumor
Aichi Cancer Center Nagoya, Japan; Aichi Medical University Nagakute, Aichi, Japan; University of Tokyo Tokyo, Japan
To the Editor-in-Chief:
In a recent issue of The American Journal of Pathology, Lawrence et al1 reported their immunohistochemical studies on ALK in inflammatory myofibroblastic tumors (IMT). They found cytoplasmic ALK expression in association with TPM3-ALK or TPM4-ALK chimeric transcript, which is a well-known feature of anaplastic large cell lymphoma (ALCL), in 6 of 11 IMT cases and nuclear ALK staining in one case. In addition, ALK-positive IMT showed a noticeably younger age distribution and had the same characteristics with ALK-positive ALCL. Their diagnosis of IMT was based only on morphological characteristics; however, the differential diagnostic examinations from T cell lymphomas such as T cell receptor gene rearrangements or expression of cytotoxic molecules were not mentioned.
It is well recognized that the morphological spectrum of ALCL is
broad2,3
and includes sarcomatoid variant ALCL, which
shows spindle shaped lymphoma cells and has a fibroblastic
appearance.4
Here, we report a case of sarcomatoid variant
of ALCL with cytoplasmic ALK expression. A six-year-old girl presented
at Aichi Medical University Hospital with axillary and supraclavicular
lymphadenopathy in May, 2000. The biopsy specimen of the axillary lymph
node showed a diffuse infiltration of spindle-shaped tumor cells with a
storiform pattern (Figure 1A)
. Although the histological appearance
resembled that for IMT,5
the restriction of the tumor to
the lymph node and occasional mimicry of ALCL in the form of
histiocytosis or carcinoma2,3
prompted us to search for
markers of lymphoid malignancies. The tumor cells were positive for ALK
(cytoplasmic, Figure 1B
), CD30, CD4, EMA, TIA-1, and granzyme B, and
negative for CD2, CD3, CD5, CD8, CD15, CD20, CD45RO, CD56, and EBV. The
patient was consequently diagnosed with sarcomatoid variant of ALCL
with null cell phenotype. However, it was of great interest that the
lymphoma cells were positive for 
-smooth muscle actin (Figure 1C)
.
Staining examination of the malignant lymphoma including bone marrow
biopsy showed no extranodal involvement of the tumor. The patient was
successfully treated with a chemotherapeutic regimen including
doxorubicin, vincristine, cyclophosphamide, and prednisone, and is
alive without disease, 10 months after the initial diagnosis.
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-Smooth muscle actin has been reported to be expressed in IMTs
6
and also in several cases of malignant
lymphoma,7,8
indicating that the -smooth muscle actin
is not a golden marker for soft tissue tumors. The positive reaction of
cytotoxic molecules on the tumor cells and the disease localization of
lymph nodes strongly suggest that the neoplasm is derived from T cells.
We therefore propose that differential diagnosis of lymphoid
malignancies including ALCL is needed for the precise diagnosis of IMT,
particularly in cases with ALK expression.
References
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