C-MYC expression analysis by immunohistochemistry in cases of subcutaneous panniculitis T-cell lymphoma and lupus panniculitis

Introduction

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare primary cutaneous T-cell lymphoma accounting for less than 1% of all primary cutaneous T-cell lymphomas.¹ Middle-aged females are twice as commonly affected as males. Varying-sized non-ulcerated nodules, especially in the lower and upper extremities, are the common presentations.² It is characterised by lobular panniculitis with sparing of the epidermis, dermis, and interlobular septae. The infiltrate is composed of CD8⁺, α-β-expressing neoplastic T-cells. Characteristically, these cells accumulate around individual adipocytes and destroy their membranes. Karyorrhexis, mitosis, and fat necrosis are commonly seen.¹ Approximately 20% of cases are associated with autoimmune disorders, especially lupus erythematosus.² Notably, a significant overlap exists between SPTCL and lupus panniculitis (LP) in clinical, histological, and immunological profiles, rendering their differentiation challenging.³ These two histologic mimics have different pathogenesis. Earlier studies have shown that the expression of c-MYC, a common proto-oncogene, differs between the two entities. However, their expression by immunohistochemistry (IHC) has yet to be extensively studied. This study aims to assess the diagnostic utility of c-MYC expression in differentiating SPTCL from LP.

Methods

All cases of SPTCL and LP diagnosed between 2015 and 2022 were retrieved from the electronic archive of the Department of Histopathology. Nine SPTCL biopsies were retrieved from seven patients. Additionally, 11 LP cases were included in the study for comparison. The slides of these cases were retrieved and reviewed. IHC for c-MYC [cell marque (Sigma Aldrich), EP121, 1:50 dilution] was performed on formalin-fixed, paraffin-embedded tissue sections. The percentage of c-MYC-positive cells was quantified. For quantification, areas with maximum c-MYC positivity were photographed under 40× magnification. Three microphotographs were evaluated. All nuclei were counted using the Image J cell counter software. Nuclei showing any level of c-MYC positivity (dim to bright) were considered positive. The percentage positivity was then calculated. Fluorescence In Situ Hybridisation (FISH) analysis for c-MYC translocation was performed using a dual-colour probe (Vysis) on two cases with the highest c-MYC positivity. Cases showing a translocated signal in more than 20% nuclei were considered positive for c-MYC translocation.

Results

We included nine biopsies of SPTCL from seven patients (one patient had three biopsies) and 11 biopsies of LP for this study. The mean age of patients with SPTCL and LP was 27.7 years (range: 10-50 years) and 35.9 years (range: 18-62 years), respectively. SPTCL affected both sexes almost equally (M:F::3:4), whereas all cases of LP were female. The histological and immunocytochemical features were evaluated. Features like rimming of adipocytes (100% vs. 54.5%), karyorrhexis (100% vs. 27.3%), and fat necrosis (88.8% vs. 36.4%) were commonly seen in SPTCL [Figures 1 and 2]. On IHC, all the SPTCL cases were positive for CD3, CD8 and negative for CD4 [Figure 2a-c]. Dermal inflammation (90.9% vs. 33.3%), septal panniculitis (63.6% vs. 33.3%), mucin deposition (27.3% vs. 0%), granulomas (9.1% vs. 0%), and giant cells (18.2% vs. 11.2%) were typical in LP [Figure 3a-c]. Various clinical and histological features have been summarised in Table 1.

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Figure 1a:

Microphotograph of subcutaneous panniculitis-like T-cell lymphoma (SPTCL) skin biopsy showing lobular panniculitis with sparing of dermis and septae (Haematoxylin & eosin, 40×).

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Figure 1b:

Medium-sized atypical lymphocytes surrounding and disrupting the adipocytes membrane (Haematoxylin & eosin, 400×).

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Figure 1c:

Prominent karyorrhectic debris is noted. (Haematoxylin & eosin, 400×).

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Figure 2a:

Immunohistochemistry in subcutaneous panniculitis-like T-cell lymphoma (SPTCL). The tumour cells are positive for CD3 (200×).

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Figure 2b:

Immunohistochemistry in subcutaneous panniculitis-like T-cell lymphoma (SPTCL). The tumour cells are positive for CD8 (200×).

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Figure 2c:

Immunohistochemistry in subcutaneous panniculitis-like T cell lymphoma (SPTCL). They are negative for CD4 (200×).

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Figure 3a:

Microphotograph of lupus panniculitis (LP) skin biopsy showing lobular panniculitis (Haematoxylin & eosin, 20×).

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Figure 3b:

Microphotograph of lupus panniculitis (LP) showing Mature-looking lymphocytes surrounding the subcutaneous adipocytes (Haematoxylin & eosin, 200×).

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Figure 3c:

Microphotograph of lupus panniculitis (LP) showing Occasional plasma cells and neutrophils are also noted, (Haematoxylin & eosin, 400×)

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c-MYC expression

The percentage of c-MYC-positive cells was evaluated. The c-MYC positivity between two groups are compared using Independent samples t-test. The c-MYC positivity was higher in cases of SPTCL with a mean of 10.6% (Standard Deviation: 6.9) and a median of 9% (range: 0.5-22%) [Table 2, Figure 2d]. The LP cases had a lower positivity rate with a mean of 1.9% (standard deviation 2.6) and a median of 1.2% (range: 0-8% ) [Table 2, Figure 3d]. The difference was highly significant with a p-value of 0.0005 [Table 2, Figure 4]. On evaluating the difference between the percentage positivity in the centre and periphery of lobules, the c-MYC positivity was significantly higher in the former (mean 15.1% vs. 5.6%; median 12% vs. 6%) with a p-value of 0.007 in cases of SPTCL. However, this difference was absent in cases of LP (mean 2.1% vs. 1.3%; median 0.5% vs. 0.5%) [Table 3, Figure 4]. One patient had three biopsies done at different intervals. The second and third biopsies were after 3 months and 3 years, respectively. The initial c-MYC positivity was 20% which reduced to 8% after 3 months of treatment. This patient had a relapse 3 years later, which showed c-MYC positivity of 22%.

Table 2: Comparison of c-MYC positivity by immunohistochemistry in subcutaneous panniculitis-like T cell lymphoma (SPTCL) and lupus panniculitis (LP)

c-MYC expression	SPTCL	LP
Range	0.5-22%	0-8%
Mean	10.6%	1.9%
Median	9%	1.2%
	p-value = 0.0005

P value is significant if <0.05

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Figure 2d:

Immunohistochemistry in subcutaneous panniculitis-like T-cell lymphoma (SPTCL). c-MYC expression in tumour cells is 20% (400×).

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Figure 3d:

Microphotograph of lupus panniculitis (LP). The percentage of c-MYC positivity is low (0%) (IHC, 400×).

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Figure 4:

A line chart showing the percentage of c-MYC positivity in the cases of subcutaneous panniculitis-like T-cell lymphoma (SPTCL) and lupus panniculitis (LP).

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Table 3: c-MYC positivity in the centre of the lobules in subcutaneous panniculitis-like T-cell lymphoma (SPTCL) and lupus panniculitis (LP) cases

c-MYC expression	SPTCL		LP
	Centre of fat lobules	Periphery of fat lobules	Centre of fat lobules	Periphery of fat lobules
Range	0.5-38%	0.5-13%	0-10%	0-6%
Mean	15.1%	5.6%	2.1%	1.3%
Median	12%	6%	0.5%	0.5%
	P-value:0.007		P-value:0.08

P value is significant if <0.05

Discussion

SPTCLs are rare T-cell lymphomas with an incidence of 1.5 cases per 10 million person-years in the United States (USA), but it has a higher incidence in Asian countries.^4,5 Middle-aged females are usually affected with a M:F ratio of 1:2-3. SPTCL, often associated with Systemic Lupus Erythematosus (SLE), makes LP a frequently encountered differential. Some believe that sometimes they coexist and a few others argue that they are the extremes of the same spectrum of disease.⁶ The management of SPTCL is different from LP. These patients frequently develop hemophagocytic lymphohistiocytosis (HLH), leading to death and necessitating aggressive treatment. Due to the importance of differentiating the two entities, many studies have explored the clinical, histological and immunohistochemical properties and have yet to establish a clear-cut difference, necessitating further exploration into the molecular studies and pathogenesis.^3,7

Histological examination of SPTCL reveals infiltration by medium-sized atypical lymphocytes in the subcutaneous tissue, particularly around adipocytes, leading to fat necrosis. Typical findings include karyorrhectic debris, haemorrhage, and increased Ki67 labelling index. In our cases, histological features such as dermal inflammation (n=10/11, 90.9%) and septal panniculitis (n=7/11, 63.6%) were prevalent in LP. In SPTCL cases, we frequently observed adipocyte rimming (n=9/9, 100%), karyorrhexis (n=9/9, 100%), and fat necrosis (n=8/9, 88.8%). Mucin deposition (n=3/11, 27.3%) and granulomas (n=1/11, 9.1%) were found exclusively in LP cases in our study. However, it is essential to note that none of these features are pathognomonic but only suggestive.³

The pathogenesis of T-cell lymphomas is less understood than B-cell lymphomas.⁸ The proto-oncogene MYC, crucial in various cellular processes, including cell cycle, metabolism, proliferation, differentiation, and apoptosis is implicated in numerous neoplastic conditions, particularly those affecting B-cells.⁹ However, the expression of c-MYC in T-cell lymphomas is not well-established. Few studies recently have noted c-MYC positivity in many T-cell lymphomas, including anaplastic large-cell lymphomas, T lymphoblastic lymphoma, extranodal NK/T cell lymphoma, and peripheral T-cell lymphomas.¹⁰ To the best of our knowledge, only one study in the past has examined the c-MYC expression in SPTCL and compared it with LP.¹¹

Fernandez et al. conducted a notable study investigating c-MYC expression through IHC in 23 SPTCL and 12 LP cases. Their findings revealed c-MYC positivity ranging from 0.8% to 16% (mean 5.0%; median 4.4%) in SPTCL cases and from 0.34% to 3.7% (mean 1.4%; median 0.8%) in LP cases with a p-value of 0.003.¹¹ Similarly, our study shows c-MYC positivity ranging from 0.5% to 22% (mean 10.6%, median 9%) in SPTCL cases and from 0% to 8% (mean 1.9%, median 1.2%) in LP cases with a highly significant p-value of 0.0005. Additionally, on evaluating the difference between the positivity in the centre and periphery of lobules in SPTCL, the c-MYC expression was significantly higher in the former (p-value: 0.007). However, this difference was absent in cases of LP, indicating that c-MYC positivity was more pronounced in areas with fat entrapment. The study by Fernandez et al.¹¹ also observed that the percentage of c-MYC-positive cells around adipocytes tended to be higher in SPTCL cases than in LP cases. They also noted heterogeneity in the same lesion and different lesions of the same patients when the biopsy was taken simultaneously from both sites. Additionally, in 4/5 cases where post-treatment biopsy was available, a decrease in c-MYC positivity was noted. However, there was no temporal relationship between the treatment and the reduction in the three cases. Also, one case showed increased c-MYC positivity and later developed HLH. This data is too small to establish any relationship between the increase in c-MYC positivity and disease progression or HLH.¹¹ In our study, follow-up biopsies were available in one case where the initial c-MYC positivity was 20%, which was reduced to 8% after 3 months of treatment. Additionally, 3 years later, the patient had a relapse, which again showed c-MYC positivity of 22%.

The SPTCL cases showing c-MYC positivity below 8% showed overlap with LP cases [Figure 5]. It is important to note that even though there is a significant difference between the c-MYC positivity between these two entities, overlap between the two cohorts remains, bringing down the practical utility of c-MYC IHC in the diagnosis. However, the positive predictive value remains. Some patients with LP progress to SPTCL over time. In this context, the patients with high c-MYC need to be followed up to see if they develop SPTCL over a long duration. If proven, c-MYC can be a valuable predictive marker.⁶

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Figure 5:

A Gaussian chart showing overlap of the percentage of c-MYC positivity in the cases of subcutaneous panniculitis-like T-cell lymphoma (SPTCL) and lupus panniculitis (LP).

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Furthermore, FISH analysis conducted on two SPTCL cases in our study did not reveal any evidence of c-MYC rearrangement or amplification, mirroring the findings of the aforementioned study. This absence of major structural changes in the chromosome implies that c-MYC signals are increased via other pathway activation. However, these require more extensive studies to confirm.

Limitations

The study limitations include the lack of follow-up, especially cases of LP with higher c-MYC, absence of FISH studies in all cases, and a smaller sample size. A T cell receptor-delta IHC stain was not performed to exclude a γ-δ T-cell lymphoma presenting with panniculitis due to non-availability.

Conclusion

This study highlights the potential clinical implications of c-MYC IHC in SPTCL and LP cases. It can be used as a supportive marker to distinguish between SPTCL and LP. The c-MYC expression, in the absence of gene rearrangements, suggests alternative mechanisms of activation that may serve as future therapeutic targets. A high c-MYC expression could be explored as a marker for more aggressive disease behaviour. If validated in larger cohorts, these findings could support using c-MYC IHC as a diagnostic adjunct and a prognostic marker.

Overall, these results contribute to our understanding of c-MYC expression patterns in T-cell lymphomas, highlighting potential differences between SPTCL and LP and emphasising the need for further investigation into the role of MYC in the pathogenesis of these diseases.