Case 4 -
Skin Biopsy, Scalp, Cutaneous Follicle Center Lymphoma, Grade 2
Randy D. Gascoyne
University of British Columbia
Vancouver, BC, Canada
Click on each slide thumbnail image for an enlarged view
A 74 year old man presented in 1988 with a raised, red skin mass involving his scalp. Following a
skin biopsy (submitted slide), complete lymphoma staging was performed. This revealed a normal LDH and
performance status and a negative bone marrow examination. There were no nodal sites of involvement.
FISH studies for the t(14;18) were negative, but IGH PCR revealed a
monoclonal B cell population.
He was diagnosed as stage 1AE and treated with radiotherapy alone. He did well and remained
lymphoma-free for nine years. In 1997 he died of unrelated causes resulting from circulatory compromise
associated with non-insulin dependent diabetes.
Case 4 - Figure 4 - CD3 stain of cutaneous follicular lymphoma.
Case 4 - Figure 5 - CD21 stain of cutaneous follicular lymphoma. Note the tight meshworks of follicular dendritic cells.
Case 4 - Figure 6 - CD10 stain of cutaneous follicular lymphoma showing strong expression.
Case 4 - Figure 7 - Bcl-6 stain of cutaneous follicular lymphoma showing weak but definite staining of neoplastic B cells.
Case 4 - Figure 8 - Bcl-2 staining of this case with strong expression.
The sections of the skin biopsy reveal a dense dermal lymphoid infiltrate with a nodular growth
pattern. The epidermis is not involved. Most of the nodules resemble lymphoid follicles and although
many contain mostly small centrocytes, some follicles with admixed centroblasts can be identified. Many
of the follicles lack intact mantle zones and tingle body macrophages. A MIB-1 stain shows a low
proliferative fraction within the follicles (data not shown). Plasma cell differentiation is not evident
and no Russell of Dutcher bodies are present. Immunostains reveal a CD20-positive tumor with
co-expression of Bcl-2, Bcl-6 and CD10. Note the presence of some CD10/Bcl-6-positive cells outside of
the follicular structures. Light chain restriction was not evident, but a CD21 stain shows the typical
tight network of follicular dendritic cells characteristic of follicular lymphoma involving lymph node
sites. Molecular studies included polymerase chain reaction (PCR) for both IGH and BCL2 loci, as well as interphase fluorescence
in situ hybridization (FISH) studies for the t(14;18). These revealed a
clonal B cell tumor, but no molecular evidence for the t(14;18) was present by either PCR or FISH.
The differential diagnosis in this case includes cutaneous lymphoid hyperplasia, the cutaneous variant
of a follicle center lymphoma (primary cutaneous follicular lymphoma) and a cutaneous marginal zone B
cell lymphoma (MZL) with follicular colonization.
Cutaneous lymphoid hyperplasia (previously known as pseudolymphoma, a term that should be abandoned),
can result from a number of causes, including arthropod bite, sites of antigen injection, Lyme disease
etc . Most often, an identifiable cause is never detected. These infiltrates may show distinct
reactive follicles, but often are vaguely nodular or diffuse. Granulomas may be seen. The cytology is
unremarkable and polyclonal plasma cells may be present in some cases. Immunostains show an intact
immuno-architecture, often with an abundance of reactive T cells . Molecular genetic studies are
particularly useful in this setting, as typically cases fail to disclose the presence of a B cell or T
cell clone. As is true of all cases of lymphoid infiltration of the skin, close correlation with the
clinical findings is mandatory. Most often these cases can be confused with cutaneous marginal zone
lymphomas. In case # 4, there was a dense dermal infiltrate with a predominance of CD20+
cells and a clonal B cell population by PCR. The follicular structures show strong expression of Bcl-2
protein. All of these findings tend to favour a diagnosis of a cutaneous B cell lymphoma.
Cutaneous marginal zone lymphoma (so-called cutaneous MALT lymphoma) is relatively common, as the skin
represents the second most common extranodal site for the development of MALT lymphomas . Often the
infiltrates are vaguely nodular, due to the presence of colonized follicles. Less commonly, well-formed
lymphoid follicles are identified with benign appearing germinal centers and intact mantle zones. The
lymphoid infiltrate occupies the marginal zones and may have the typical cytology of MZLs with small
cells showing nuclear irregularity and abundant amounts of pale clear cytoplasm. Occasional admixed
larger cells are frequently present. An extra-follicular plasma cell population may be seen in some
cases, and may be shown to be part of the neoplastic clone following stains for kappa and lambda light
chains. The typical cytology of follicle center cells is not present in the majority of MZL cases.
Immunostains of particular value in the differential diagnosis include Bcl-2, Bcl-6, CD10 and CD21 .
Stains for kappa and lambda can also be of value. Follicles can be shown to be clearly benign
(Bcl-6+/CD10+ and Bcl-2-negative), a finding that favours a cutaneous MZL, or show
follicular colonization with vaguely defined follicular structures with alternating B cells
(Bcl-6+, Bcl-2-negative) of the germinal center and the neoplastic MZL (Bcl-6-negative,
Bcl-2+). Stains for follicular dendritic cells (FDC) (CD21, CD23, CD35 or CNA42) are useful
for demonstrating these expanded/colonized FDC meshworks. Absence of staining of B cells in the
interfollicular zones with either Bcl-6 or CD10 tends also to favour a MZL. PCR studies for IGH clonality are useful for distinguishing cutaneous lymphoid hyperplasia, which
typically lacks evidence of a clonal proliferation. Interphase FISH or PCR studies for the t(14;18)
would be expected to be negative in cutaneous MZLs. Standard cytogenetic analyses must be interpreted
with caution, as the presence of a typical t(14;18) can be seen in MALT lymphomas involving skin .
Importantly, the breakpoint on chromosome 18 does not involve the BCL2
oncogene, but involves the MALT gene lying 5 MB centromeric of BCL2
. Other dual-color FISH assays may be of value in the differential
diagnosis, including probes for the t(11;18)(q21;q21) and t(3;14)(p14;q32), either of which may be
positive in cutaneous MALT lymphomas. The combination of morphological findings and immunophenotype in
this case favour a primary cutaneous follicular lymphoma over a MALT lymphoma.
Primary cutaneous follicle center lymphoma, often referred to as primary cutaneous follicular lymphoma
(PCFL), is now recognized as a distinct disease entity and a variant of nodal FL in the WHO
classification . Such cases are recognized by primary cutaneous presentations, absence of
extra-cutaneous disease within six months of diagnosis and frequent involvement of the head & neck.
In the author's experience, this subtype of cutaneous B cell lymphoma is much less common than cutaneous
Much confusion in the literature exists regarding the existence of PCFL, due in part to the use of two
common classification schemes throughout the world
. The European Organization for Research and
Treatment of Cancer (EORTC) recognizes primary cutaneous follicle center cell lymphoma (PCFCCL) as a
morphological entity based on the cytological appearance of the cells (mixture of centrocytes and
centroblasts) and largely ignores architecture as a defining feature. In contrast, the WHO
classification requires that the infiltrate have at least a partially follicular growth pattern. Without
doubt, many previous studies based on EORTC criteria include a heterogeneous mix of tumor types,
including cutaneous diffuse large B cell lymphomas and cutaneous MZLs. Thus, comparing and contrasting
immunophenotypic and molecular/cytogenetic frequency data between PCFL and PCFCCL is virtually impossible
and often misleading. The majority of PCFCCL studies employing the EORTC classification show findings
completely different from nodal FL. Most cases lack CD10 expression, rarely express Bcl-2 protein and
are not associated with the t(14;18)
. In contrast, studies based on the WHO classification
typically reveal an immunophenotype characteristic of a follicular center cell derivation with expression
of both CD10 and Bcl-6; frequent expression of Bcl-2 protein and a significant minority of cases
harbouring a t(14;18) typical of nodal FL
. Although it remains possible that geographic
differences between Europe and North America account for these divergent findings, significant
differences in the EORTC inclusion criteria and the resulting heterogeneity of PCFCCL more likely
contribute to the apparent biological differences in previous reports.
Clinically, PCFL occurs in older patients (median age 63-65 years), produces solitary or grouped
papules and/or plaques and often involves the head & neck (especially the scalp) and occasionally the
trunk. Lesions are confined to the skin and by definition, extra-cutaneous involvement is not detected
at or within six months of diagnosis. Patients may relapse, but lengthy overall survival is typical.
PCFL typically produce a nodular infiltrate characterized by neoplastic follicles. Grade 3 cytology is
more frequent in comparison to nodal FL, and the presence of large centrocytes is also a feature of PCFL.
A floral pattern has recently been described more commonly in PCFL . Immunostains reveal the uniform
expression of CD20 and CD79a. FDC stains demonstrate the characteristic FDC meshworks of FL in most
cases. If one focuses on studies wherein at least a partially follicular architecture is required, then
virtually all cases express both Bcl-6 and CD10. The presence of CD10+ and Bcl-6+
cells in the interfollicular zones is also a helpful differential diagnostic feature favouring PCFL.
Similarly, Bcl-2 is variably expressed, with reports ranging from 0 to almost 90% of cases. Most series
demonstrate approximately 50% of cases with Bcl-2 expression
. Positivity often correlates
with grade, more frequently expressed by the neoplastic cells in grade 1 & 2 PCFL .
The majority of North American studies of PCFL have demonstrated the presence of the t(14;18) in
approximately 20-35% of cases
. Results vary somewhat depending on the methodology. PCR studies
are less reliable for two main reasons; they may be too sensitive and thus be associated with
false-positive results, or alternatively under-estimate the frequency of t(14;18) because of
false-negative results. These data remain controversial, as evidenced by two recent studies. A study of
30 cases from Europe restricted to cases with at least a partial follicular architecture found evidence
of BCL2 translocations by PCR in 30% of cases, but all were
FISH-negative . These data suggested that the PCR positivity resulted from bystander lymphocytes,
supporting the conclusion that the t(14;18) is not characteristic of PCFL. However, a very recent study
from North America used FISH to document the presence of the t(14;18) in PCFL in 31% of cases, suggesting
an overlap between some cases of PCFL and nodal FL . These data were compared to cases of secondary
cutaneous FL allowing the authors to conclude that PCFL more frequently lack expression of Bcl-2 and
often lack the t(14;18) translocation.
In summary, case # 4 shows findings most consistent with PCFL. The case lacks FISH evidence of a
t(14;18), but strongly expresses Bcl-2 protein, indicating the importance of other mechanisms besides
translocation that lead to deregulated Bcl-2 expression in FL.
Diagnosis: Skin biopsy, scalp, cutaneous follicle center lymphoma, grade 2
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