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| Web: | mayocliniclabs.com |
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| Email: | mcl@mayo.edu |
| Telephone: | 800-533-1710 |
| International: | +1 855-379-3115 |
| Values are valid only on day of printing | |
A 25-year-old woman presented with a palpable breast mass that was excised. Hematoxylin and eosin and immunohistochemical-stained slides of the mass are shown in the figures below.
The correct answer is ...
Dermatofibrosarcoma protuberans.
The histologic sections in this case confirm a monomorphic spindle cell proliferation with a storiform architecture. While submitted as a “breast biopsy,” the lesion is centered in the subcutis, and no breast epithelium proper is present. The nuclei are uniform with minimal cytologic atypia, and mitotic activity is low. Infiltration and entrapment of adipose tissue in a honeycombing pattern is well-demonstrated.
By immunohistochemistry (IHC), the neoplastic cells are diffusely positive with CD34, while negative with STAT6. The overall morphology and immunophenotype are most consistent with dermatofibrosarcoma protuberans (DFSP).
DFSP is an uncommon and locally aggressive neoplasm that is most commonly encountered in the dermis and subcutaneous tissues of the skin. Rarely, DFSP may present as a deeper-seated lesion. It is characterized by diffuse infiltration with a honeycombing pattern of entrapment of adipose tissue. The neoplastic cells are uniform with plump to elongated nuclei and with a whorled storiform histoarchitecture.1,2 Fibrosarcomatous differentiation can infrequently occur, with a more nodular and fascicular appearance of cells with cytologic atypia and increased mitotic activity.3
By IHC, DFSP is strongly and diffusely positive for CD34, a reliably sensitive but not specific marker.2 It is most frequently characterized by a t(17;22)(q22;q13) COL1A1-PDGFB fusion. Rare cases may be negative for PDGFB rearrangements by fluorescence in situ hybridization (FISH), as in this case. They may instead harbor fusions involving PDGFD, which has been observed in some cases of DFSP occurring in the breast.4
Primary sarcomas, especially other than phyllodes tumors, of the breast are exceedingly rare, comprising <0.1% of all breast malignancies. Nonetheless, sarcomas may be encountered in both breast biopsies and excisions. Ancillary testing may be necessary to rule out the differential diagnosis of metaplastic (spindle cell) carcinoma. The subcutaneous/dermal location of the lesion in this case, combined with histologic features and IHC results, allowed for a specific diagnosis of DFSP. While locally aggressive and prone to local recurrence (up to 60%), distant metastases from DFSP are rare.2,3
Kaitlyn Nielson, M.D.
Fellow, Surgical Pathology
Mayo Clinic
Charles Sturgis, M.D.
Consultant, Anatomic Pathology
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science
A 79-year-old woman presented with a palpable left breast mass. Mammogram confirmed a well-circumscribed nodule within the breast corresponding to the palpable abnormality. She underwent a biopsy and a subsequent partial mastectomy.
The correct answer is ...
Cylindroma.
The occurrence of primary breast neoplasms with eccrine and apocrine phenotypes has been described and supports the notion that breast is a modified sweat gland. One of those entities is a cylindroma, which is a benign often dermal-based neoplasm that is most commonly encountered on the neck, head, and scalp of middle-aged and elderly females. These tumors are uncommon in the breast. Both breast and dermal cylindromas share histomorphologic and immunohistochemical features. These tumors are nonencapsulated but well-demarcated lesions that show a characteristic “jigsaw” pattern of epithelial nests. The epithelial nests are composed of central luminal cells and peripheral myoepithelial cells. Mitotic activity is generally absent and nuclear pleomorphism is minimal. The nests of cells are surrounded by a thickened band of basement membrane material. Globules of hyaline basement membrane material may be present in the interior of the epithelial nests. The epithelial cells are immunoreactive with markers typically expected to be positive in ductal epithelium of the breast, including GATA3 and CK7, whereas the peripheral cells show positivity with myoepithelial cell markers such as p63. Cylindromas may show aberrant MYB-NFIB fusion transcripts.
Breast cylindromas show overlapping features and marker positivity with other entities such as adenoid cystic carcinomas and basaloid invasive ductal carcinomas; therefore, correlations with clinical presentation, imaging studies, patient history, and careful microscopic evaluation are of utmost importance to arrive at accurate diagnoses.
Patricija Zot, M.D.
Fellow, Surgical Pathology
Mayo Clinic
Charles Sturgis, M.D.
Consultant, Anatomic Pathology
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science
A 57-year-old man presented to his primary physician complaining of three weeks of sudden-onset “profound fatigue” and dyspnea on exertion. His medical history is insignificant. Initial laboratory studies (Figure 1a) are remarkable for a markedly elevated erythrocyte sedimentation rate and rouleaux formation in the CBC manual differential (Figure 1b), and serum hyperviscosity (Figure 2). Serum protein electrophoresis exhibited an M-spike of 3.4 g/dL and isotyping via MALDI-TOF mass spectrometry identified a monoclonal IgM kappa protein (Figure 1c/d).
The correct answer is ...
Lymphoplasmacytic lymphoma.
Matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) is the method utilized at Mayo Clinic for M-protein isotyping, termed Mass-Fix (available since 2018 for clinical testing). It has replaced the traditional immunofixation electrophoresis (IFE) method for isotyping the M-protein identified by serum protein electrophoresis (SPE). Serum samples are immunopurified using five separate immunoglobulin (Ig) enrichment beads specific for IgG, IgA, IgM, and the two light chains, kappa and lambda. Following elution and a reduction step of each Ig-enrichment into heavy and light chains, the samples are spotted onto steel plates with matrix, and a laser ionizes each sample. The overlay of the resulting spectra (as seen in Figure 1d) is in a similar format to that of IFE and allows for isotyping of any monoclonal proteins in the specimen. Normal patients have near-gaussian mass-to-charge (m/z) distributions of light chains (lambda has one while kappa has two, corresponding to the two variant germ line kappa genes with one several amino acids heavier than the other). A patient with a monoclonal protein (M-protein) exhibits a spike in the light chain m/z distribution, and by inspecting all five spectra overlaid, one can determine the isotype of the M-protein.
Lymphoplasmacytic lymphoma (LPL)
A mature B cell lymphoma that is uncommon (only ~1% of hematologic malignancies in US), LPL is further characterized by the isotype of the clonal immunoglobulin secreted. When an IgM monoclonal gammopathy is present, is termed Waldenström macroglobulinemia (WM). Genomics studies show that LPL is phenotypically more comparable to chronic lymphocytic leukemia (CLL) than multiple myeloma (MM). The most common mutation seen in LPL is an activating point mutation (L256P) of MYD88, contributing to pathogenesis. Unfortunately, patients present with diverse symptoms, including most commonly weakness and fatigue (secondary to anemia), fever, diaphoresis, and weight loss (though around one-third of patients are asymptomatic at diagnosis). At diagnosis, over 70% of patients are in stage IV disease (as defined by involvement of the bone marrow). In the laboratory, the majority of patients exhibit a monoclonal gammopathy on serum protein electrophoresis or immunofixation. The monoclonal immunoglobulin class helps determine subtype of LPL and prognosis. For example, patients with a monoclonal IgM in their serum are diagnosed as having the clinical syndrome WM (more rare, with around 1,400 new cases per year in the U.S.). The original tumor can also produce different immunoglobulins, a mixed population of immunoglobulins (IgG and IgM, for example), mixed cryoglobulins and gamma heavy chains. Patients with an IgG monoclonal protein have a less aggressive clinical course compared to other classes.
This patient’s monoclonal gammopathy was isotyped as an IgM-kappa, with an M-spike of 3.4 g/dL. The initial concerning laboratory result was his elevated SED rate and manual differential, showing rouleaux formation, a linear stack of red blood cells that forms in the presence of high plasma protein concentrations. Further investigation yielded the laboratory results shown in Figures 1 and 2. He also exhibited bilateral retinal hemorrhages. Hyperviscosity is common with a diagnosis of WM, as IgM molecules form pentamers. The target of the IgM clone suggests further symptoms or associated diagnoses, such as anti-nerve components resulting in neuropathy or anti-red blood cells leading to autoimmune cold hemolytic anemia. His initial chief complaints are consistent with WM. Tumor infiltration of the tissue can lead to lymphadenopathy, hepatomegaly, and splenomegaly. A bone marrow aspirate was microscopically analyzed (low grade B-cell lymphoma with plasmacytic differentiation, 90%-95% cellular involvement of the marrow with 6% plasma cells), then genotyped and found positive for an activating mutation in MYD88. Due to the patient’s symptomatic presentation and initial IgM of 6,380 mg/dL, two sessions of plasma exchange were performed which reduced his IgM first to 3,890 mg/dL and finally to 1,850 mg/dL. His IgM concentrations rebounded quickly after plasma exchange and each early dose of drug therapy.
The 57-year-old man, who initially presented with profound fatigue, headache, weight loss, and tinnitus, received chemotherapy and careful monitoring of serum IgM concentration.
Multiple myeloma (MM)
Over 10 times more prevalent than LPL, multiple myeloma (MM) makes up 10% of hematologic malignancies and it currently has no cure (though remission is possible). While LPL is cancer of white blood cells in the lymph system, MM is localized to the bone marrow (BM). IgM MM is very rare. Arising from an aberrant clone of BM plasma cells, MM is almost always preceded by a premalignant, asymptomatic condition called monoclonal gammopathy of undetermined significance (MGUS). Unlike MGUS, MM may be characterized by the CRAB criteria: hypercalcemia, renal dysfunction, anemia, and bone lesions. Another pre-malignant, intermediate stage of disease, termed smoldering MM (SMM), occurs when patients remain asymptomatic but meet the laboratory criteria for MM (i.e., an M-spike of >3 gdL, between 10%-60% bone marrow plasma cells, and no evidence of end-organ damage or amyloidosis). Diagnosis of MM requires >10% clonal plasma cells on bony or soft tissue plasmacytoma, plus one of the following additional characteristics: presence of any of the CRAB criteria or a biomarker associated with eventual end-organ damage (>60% bone marrow plasma cells, involved free light chain ratio >=100 or presence of one or more bone lesions on imaging).
In addition to the CRAB signs and symptoms, MM patients may rarely have neurological manifestations. MM patients are more susceptible to infections due to immune dysfunction. The detection of monoclonal proteins is paramount to diagnosing MM, and the laboratory methods include serum and urine protein electrophoresis and immunofixation. At Mayo Clinic, MALDI-TOF mass spectrometry is utilized for isotyping the monoclonal protein. Measuring free light chains in serum is not only part of the diagnostic criteria, but also used to monitor response to therapy; nephelometric or immunometric assays (ELISA) are available for quantitation. There are several phenotypes of MM: those characterized by a single immunoglobulin population (IgG-kappa is the most common), biclonal disease, light chain myeloma, and both oligo-secretory and nonsecretory forms of MM. All phenotypes can be differentiated by various laboratory tests, including serum and urine M-protein concentration, isotyping of the monoclonal protein, and bone marrow biopsy interpretation (including percent clonality and light chain restriction).
Immunoglobulin light chain amyloidosis (AL amyloidosis)
AL amyloidosis is a rare systemic disorder whose prevalence is unknown and can present as unexplained heart failure, heavy proteinuria, edema, and hepatosplenomegaly. Nonspecific symptoms, such as weight loss and fatigue, are common with AL amyloidosis. There are several forms of amyloidosis, as the term describes tissue deposition of protein fibrils (various subunits of normal serum proteins). When these fibrils are made of monoclonal immunoglobulin light chains, the diagnosis is AL amyloidosis, and it can present alone or in combination with other plasma cell proliferative disorders (such as MM or WM) or lymphomas. The degree of end-organ damage varies dramatically, from only one organ to widespread multi-system damage, with the kidneys being most commonly involved. Of note, AL amyloidosis can be a rare complication of an IgM-associated gammopathy, such as WM.
The diagnosis requires clinical or laboratory evidence of a plasmacytic proliferative disorder (e.g., serum or urine M-protein, elevated FLC ratio in serum, or clonal plasma cells in bone marrow) and positive Congo red staining in a tissue or bone marrow biopsy. Most patients with AL amyloidosis exhibit elevated monoclonal immunoglobulins, either IgG or free light chain isotypes. The same laboratory examinations used to detect MM are applied when AL amyloidosis is suspected. This patient does not have marked proteinuria or end-organ damage associated with AL amyloidosis.
Monoclonal gammopathy of undetermined significance (MGUS)
Approximately 3% of adults over age 50 have a MGUS and it is often discovered incidentally during evaluation for a number of other disorders, as it is asymptomatic. This patient had significant symptoms at presentation. Of the three subtypes of MGUS, non-IgM MGUS is the most prevalent followed by IgM MGUS, and finally light chain MGUS (LC-MGUS). While nearly all MM patients had a MGUS diagnosis prior, not all MGUS progresses to a more sinister plasma cell proliferative disorder. The diagnostic criteria for MGUS includes a serum M-protein (<3 g/dL), lack of end-organ damage, and if a bone marrow biopsy was performed, <10% plasma cell monoclonality. Many of the studies on MGUS progression were conducted at Mayo Clinic, starting in the 1960s, by Dr. Robert Kyle. The rate of progression of MGUS into advanced disease is 1% per year, yet 6.5 times more MGUS patients developed MM, WM, amyloidosis, or another lymphoproliferative disorder compared to the general population.
Ria Fyffe-Freil, Ph.D.
Fellow, Clinical Chemistry
Mayo Clinic
@rcfsquaredPhD
Maria Alice Willrich, Ph.D.
Consultant, Clinical Biochemistry
Mayo Clinic
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science
@malicewi
A 46-year-old man presented with decreased hearing and feelings of “stuffiness” in his left ear. He was found to have two enlarged lymph nodes in his left neck, both measuring 3 cm. He underwent an FNA of one of the lymph nodes.
The correct answer is ...
Metastatic lymphoepithelial carcinoma.
Lymphoepithelial carcinoma (LEC) is a rare, poorly differentiated carcinoma resembling non-keratinizing squamous carcinoma, with an associated prominent nonneoplastic lymphoplasmacytic infiltrate. The malignant cells have large nuclei with prominent nucleoli, and high nuclear-to-cytoplasmic ratios. They can be polygonal with indistinct cell borders. In some cases, the reactive lymphocyte population can equal or appear more prominent than the malignant cells.
Immunohistochemistry (IHC) demonstrates expression of pan-keratin and other squamous markers (i.e., AE1/AE3, ck Oscar, p40, p63, and CK5/6), with no expression for S100, SOX10, CKR7, and CD68. The lymphoplasmacytic infiltrate shows positivity for CD45.
LEC most commonly occurs in the nasopharynx, but can be found throughout the head and neck, including the salivary glands, oral cavity, paranasal sinuses, oropharynx, larynx, esophagus, and lungs. Metastases to regional lymph nodes are more common in salivary LEC, as up to 40% of patients with salivary lesions present with cervical lymph node involvement. Local spread without metastases is more common in sinonasal cases.
Most cases are associated with Ebstein-Barr virus (EBV), and are more common in populations with endemic EBV, such as Southeast Asia and Arctic Inuit communities. The patient in this case was an Asian male. In contrast, in non-endemic populations such as the United States and Japan, EBV association is less common. Of note, while EBV plays an important role in the pathogenesis of this malignancy, it does not appear to be prognostically relevant.
Overall, cases of LEC occur predominantly in men 40-82 years of age, but sex predilection and age of onset differ by primary site. For example, the LEC originating from the salivary gland tends to occur in the fifth decade of life and has a roughly equal prevalence in male and female patients, whereas nasopharyngeal LEC has a higher prevalence in males.
The clinical presentation of LEC varies by location and can include nasal obstruction, epistaxis, facial swelling, neck mass, anosmia, or cranial nerve palsy. Surgical resection and radiation therapy are the primary treatment modalities for this malignancy. The prognosis is similar to squamous carcinoma.
Jane Jarshaw, M.D., M.P.H.
Resident, Anatomic & Clinical Pathology
Mayo Clinic
Charles Sturgis, M.D.
Consultant, Anatomic Pathology
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science
A 20-year-old woman with no significant past medical history presented with 14.5 cm ovarian mass. She underwent an oophorectomy. Grossly, the ovarian mass shows yellow to white, firm cut surface. Representative sections of the ovarian mass depicted below, along with the selected immunohistochemical stains.
The correct answer is ...
Sclerosing stromal tumor.
Sclerosing stromal tumor are uncommon ovarian tumors that occur generally in young woman and girls with a mean age of 29 years. These tumors range in size from 1.5 cm to 19 cm. Gross examination, they are generally well circumscribed and have a yellow to white solid cut surface. They often show areas of central edema with cystic degeneration.
Microscopically, these tumors have pseudolobular appearance, with alternating hypocellular myxoid edematous areas and cellular areas with collagenized zones. They typically show abundant, thin-walled, dilated vessels with prominent branching, often with a hemangiopericytoma-like appearance. In the cellular areas, spindle-shaped cells and polygonal luteinized cells are present. The luteinized cells show eosinophilic to clear vacuolated cytoplasm, round nuclei, and prominent nucleoli. Occasionally the luteinized cells may have signet ring cell appearance, especially during pregnancy. Scant spindle cells with pale cytoplasm and elongated nuclei are also usually present. Mitotic activity is generally low.
Sclerosing stromal tumor are usually positive for sex cord markers, such as inhibin, calretinin, or SF1 but are negative for cytokeratin and EMA. Recent studies have shown that a subset of these cases shows TFE3 expression.
The differential diagnosis includes other sex cord stromal tumors including fibrothecoma, microcystic stromal tumor, and adult granulosa cell tumor. Some tumors that demonstrate vacuolated cytoplasm may mimic metastatic signet ring adenocarcinoma. Fibrothecoma typically occur in peri- or postmenopausal woman with abnormal bleeding. Grossly the tumor demonstrates a uniform white cut surface. They typically lack the luteinized cells present in sclerosing stromal tumor and do not show the characteristic hemangiopericytoma like vasculature.
Microcystic stromal tumor is a benign ovarian tumor with striking microcystic growth. These tumors show admixture of microcysts, solid areas, and collagenous bands. They can often show bizarre nuclei in up to 60% of the cases. These tumors are usually very focally and weakly positive for inhibin and calretinin.
The adult granulosa cell tumor can show variety of growth patterns and should be considered in differential diagnosis for sclerosing stromal tumor. The adult granulosa cell tumor shows FOXL2 mutation in approximately 90% of the cases and can help in the diagnosis. Metastatic adenocarcinoma can be excluded by immunohistochemical studies (EMA positive and with specific epithelial markers such as CDX2, CK20, MOC31, as well as mucin stains).
Raima Memon, M.B.B.S.
Fellow, Surgical Pathology
Mayo Clinic
@rmemon1990
Amy Clayton, M.D.
Consultant, Anatomic Pathology
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science
A two-month-old infant girl, newly diagnosed with acute myeloid leukemia (AML), underwent genetic testing with conventional chromosome and AML fluorescence in situ hybridization (FISH) panel testing. Conventional chromosome analysis revealed a normal karyotype (46,XX) in 20 analyzed cells (Figure 1). While no evidence of a KMT2A (formerly MLL) rearrangement was seen with a break-apart FISH strategy (Figure 2A), a dual-color dual fusion probe set revealed a MLLT10::KMT2A fusion signal in 33% of analyzed nuclei (Figure 2B).
The correct answer is ...
These results support the presence of a cytogenetically cryptic and atypical MLLT10::KMT2A fusion which is associated with an unfavorable prognosis in pediatric AML.
Pediatric acute myeloid leukemia (AML) is a rare and genetically heterogeneous disorder. AML occurring in infants less than 1-2 years of age constitutes a specific subgroup of disease. Amongst others, this entity is characterized by a distinct genetic profile with rearrangements involving the KMT2A (formerly known as MLL) gene at 11q23 representing the most frequent cytogenetic alteration in this patient population. These are documented in approximately 50% of cases.
KMT2A rearrangements juxtapose KMT2A, a gene involved in transcriptional regulation and chromatin modification, with one of numerous partner genes, yielding a chimeric fusion oncoprotein which contributes to oncogenesis via several pathways such as enhanced transcriptional activity and aberrant promoter-like epigenetic signatures. Common KMT2A rearrangement partners in pediatric AML include, amongst others, MLLT3, MLLT10, MLLT4, ELL,MLLT1, AFF1, and MLLT11.
Classically, KMT2A rearrangements occur through reciprocal translocation events. These structural abnormalities may be detectable by conventional chromosome analysis depending on the size of the translocated segments and the achieved resolution of the chromosome banded study. On FISH analysis, KMT2A rearrangements can be detected with either 1) break-apart probes (BAPs), where a disruption of KMT2A is seen as single separate red (R) and green (G) signals, or 2) dual-color dual-fusion probes, where specific KMT2A fusions are seen by FISH patterns showing 1 red (R), 1 green (G), and 2 fusion (F) signals, which are typical findings of reciprocal KMT2A translocations. However, more complex or atypical rearrangements involving KMT2A are also observed. These include, amongst others, subtle insertions of KMT2A segments into other chromosomes and of partner gene segments into KMT2A, inversion events, complex translocations, or translocations with accompanying deletions. Thus, these atypical rearrangements may elude detection by some conventional cytogenetics methodologies (i.e., be “cytogenetically cryptic”) and show atypical FISH probe signal patterns, as seen in this case.
The presented case serves as an example of such cryptic KMT2A rearrangements as no abnormalities were apparent on conventional chromosome analysis and on KMT2A BAP FISH. Nonetheless, a KMT2A::MLLT10 fusion signal (with a 1R2G1F-pattern) was detected with dual-color dual-fusion FISH, a finding which is in support of a KMT2A rearrangement. Compared to KMT2A BAP, dual-color dual-fusion probe strategies are more sensitive and specific, as they label KMT2A and its target rearrangement partner in different colors. While the mechanisms underlying the observed pattern in the presented case cannot be ascertained in the absence of higher-resolution genetic testing, it could be attributable to a small-size insertion of MLLT10 into KMT2A. Small insertions of partner regions within KMT2A preclude sufficient separation of the KMT2A BAP FISH probes to be detected, thus remaining below the resolution of conventional chromosome analysis and BAP FISH probes.
Accordingly, the results obtained in this case support the presence of a MLLT10::KMT2A fusion event, which was cryptic by G-banding analysis and with KMT2A BAP FISH. While KMT2A rearrangements with different rearrangement partners may variably impact prognosis, KMT2A::MLLT10 rearrangements are generally considered to confer unfavorable prognostic implications in pediatric AML.
Marie-France Gagnon, M.D.
Fellow, Laboratory Genetics and Genomics
Mayo Clinic
Cinthya Zepeda Mendoza, Ph.D.
Senior Associate Consultant, Hematopathology
Mayo Clinic
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science
@CinthyaZepeda
Patient is a 50-year-old man with a sinonasal mass. In addition to the above ancillary studies, lesional cells express cytokeratin AE1/AE3 and p63 while negative for NUT, androgen receptor, synaptophysin, chromogranin, Melan-A, and mucicarmine. INI-1 and BRG-1 show retained nuclear expression.
The correct answer is ...
HPV-related multiphenotypic sinonasal carcinoma.
By definition, HPV-related multiphenotypic sinonasal carcinoma (HMSC) is a high-risk HPV associated epithelial neoplasm that shows both surface and minor salivary gland derived elements. The tumor typically affects adults (mean age 54 years) with the vast majority occurring in the nasal cavity. Multiphenotypic refers to a mixed ductal and myoepithelial morphologic and immunophenotypic phenotype.
By histomorphology, HMSC may resemble biphasic salivary gland carcinomas with tumor cells arranged in trabecular, cribriform, microcystic, or nested patterns. The myoepithelial component of the tumor is usually comprised of basaloid-appearing tumor cells. Myoepithelial cells with spindle, plasmacytoid, or clear cell change may be present. Myxohyaline stroma is frequently present in the background. A variable number of ducts are present, which may be difficult to observe due to compression by the surrounded myoepithelial cells or due to their sparse representation. The ducts typically contain more abundant eosinophilic cytoplasm. HMSC frequently shows high grade features including high mitotic activity and necrosis. Despite its high-grade appearance, HMSC exhibits indolent behavior though local recurrences are common (approximately 33%).
Surface involvement by dysplasia or carcinoma in situ may be present. Identification of surface involvement is a useful finding in the differential diagnosis of HMSC. Bone invasion is frequently seen but perineural and lymphovascular invasions are rare.
Immunohistochemically, HMSC shows evidence of both myoepithelial and ductal differentiation. Myoepithelial cell differentiation can be highlighted with p40, SMA, calponin and p63. Stains for low molecular weight cytokeratin or CD117 may preferentially highlight ducts. Immunostains for S100 and SOX-10 may highlight both cell types of the tumor. Evidence of transcriptionally active high-risk HPV can be shown with block-like p16 expression (surrogate) and high-risk HPV in-situ hybridization studies.
By morphologic findings alone, HMSC may be difficult to distinguish from salivary gland carcinomas with biphasic differentiation such as adenoid cystic carcinoma (AdCC). However, AdCC (and other salivary gland tumors) are typically not associated with overlying dysplasia or carcinoma in situ. The presence of high-risk HPV (confirmed in situ hybridization) is characteristic of HMSC.
HPV-associated squamous cell carcinoma should not exhibit morphologic and immunophenotypic evidence of a dual cell population. In this case, CK7, p63, and S100 expression provide immunophenotypic evidence of ductal and myoepithelial differentiation.
Sinonasal undifferentiated carcinoma (SNUC) is by definition an undifferentiated carcinoma lacking squamous and glandular elements. SNUC carries a much higher mortality rate then HMSC. Though SNUC may show similar nested to lobular growth patterns, high-grade cytologic features, and keratin expression, these tumors are otherwise immunophenotypically distinct. SNUC is negative for p40 and CK5/6 (evidence of squamous differentiation). S100 and SOX-10 are also negative in SNUC.
Michael McCarthy, M.D.
Resident, Anatomic and Clinical Pathology
Mayo Clinic
Michael Rivera, M.D.
Consultant, Anatomic Pathology
Mayo Clinic
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science
