Chondroid Syringoma (Cutaneous Mixed Tumor)
Chondroid syringoma (cutaneous mixed tumor), often called apocrine mixed tumor of the skin, is a rare benign adnexal tumor. It shows biphasic proliferation: a sweat-duct component of epithelial and myoepithelial cells (epithelial/myoepithelial element) mixed with a mucoid, cartilage-like stroma (chondromyxoid stroma).
Much like the salivary gland mixed tumor (pleomorphic adenoma), chondroid syringoma arises from multipotent cells in the secretory or ductal part of a sweat gland. Most cases (80–90%) come from the apocrine system; the eccrine type is less common.
PLAG1 and HMGA2 Gene Rearrangements
- PLAG1 rearrangement (pleomorphic adenoma gene 1, 8q12): Translocation places PLAG1 under the control of strongly active promoters (such as CTNNB1 or LIFR), leading to overexpression of the PLAG1 transcription factor. This is the core molecular driver that makes myoepithelial cells proliferate and secrete extracellular matrix.
- HMGA2 rearrangement (12q14–15): In tumors without a PLAG1 rearrangement, HMGA2 rearrangements are found instead. They remodel chromatin and switch on tumor cell proliferation pathways.
Epithelial–Stromal Transition and Cartilage-Like Matrix Formation (Chondrogenesis)
- The myoepithelial cells lining the outside of the ducts change shape into plasma cell-like forms (plasmacytoid / hyaline myoepithelial cells).
- These cells release large amounts of chondroitin-6-sulfate and hyaluronic acid into the surrounding matrix. This builds up as a myxoid matrix that later becomes protein-rich and turns into a hyaline cartilage-like stroma, with cells sitting in small spaces called lacunae.
Although benign, chondroid syringoma sits deep (in the deep dermis or subcutaneous fat) and can recur or, very rarely, become malignant (malignant chondroid syringoma). At Haute-Derma, our management plan includes:
- Detailed imaging: 50 MHz skin ultrasound to map the tumor's borders relative to the facial muscle fascia and nerves.
- Surgical excision with clear (R0) margins: Removing the whole tumor together with its fibrous capsule by enucleation, or by Mohs surgery when the tumor is in a difficult site (nasal ala, ear rim, upper lip).
Histopathology and Immunohistochemistry (IHC) Criteria
Histological Subtypes (Apocrine vs Eccrine)
Under the light microscope, chondroid syringoma has a distinctive biphasic appearance:
- Apocrine type (apocrine chondroid syringoma, the most common type):
- Epithelial component: complex branching ducts, cystically dilated ducts, or cords and nests of cells.
- Two cell layers: the lumen is lined by inner columnar or cuboidal cells showing decapitation secretion, surrounded by an outer layer of flattened myoepithelial cells.
- Stromal component: abundant stroma that shifts gradually from myxoid to hyaline chondroid with lacunae, and on to fibrosis, calcification or bone formation (osseous metaplasia).
- Eccrine type (eccrine chondroid syringoma, less common):
- Epithelial component: small, simple ducts of uniform diameter, lined by a single layer of epithelial cells and scattered through a chondromyxoid stroma.
- Nuclear and cellular features: Epithelial and myoepithelial cells show no nuclear atypia, mitoses are very rare (< 1–2 per 10 HPF), and there is no spotty necrosis or vascular or perineural invasion.
Diagnostic Immunohistochemistry (IHC) Markers
| IHC Marker / Stain | Where It Stains in the Tumor | Diagnostic Significance |
|---|---|---|
| S100 / GFAP | Myoepithelial cells and cells within the cartilage-like matrix | Strongly positive (+++); confirms myoepithelial origin and chondroid stroma |
| p63 / Calponin / SMA | Myoepithelial cells at the outer rim of the ducts | Clearly positive (++); confirms a preserved myoepithelial layer |
| CK7 / CEA / EMA | Epithelial cells lining the duct lumen | Strongly positive (+++); confirms sweat duct differentiation |
| PLAG1 | Nuclei of epithelial and myoepithelial cells | Positive (+); confirms the genetic change characteristic of chondroid syringoma |
| Ki-67 index | Nuclei of dividing tumor cells | Very low (< 2–5%); reflects benign growth |
High-Frequency Skin Ultrasound and Dermoscopy Criteria
- High-frequency skin ultrasound (20–50 MHz):
- Shape and borders: a round or multilobulated nodule with very sharp borders and a thin, continuous fibrous capsule, located in the deep dermis or subcutaneous fat.
- Echo pattern: heterogeneous hypoechoic structure, reflecting a mix of myxoid areas (hypoechoic) and cartilage or calcified areas (hyperechoic with faint acoustic shadowing).
- Posterior acoustic enhancement: clearly present, because the myxoid stroma transmits sound well.
- Color Doppler: little or no internal blood flow, or only low-resistance microvessels at the periphery.
- Dermoscopy:
- Background: a dome-shaped area that is uniformly skin-colored, pale pink or whitish yellow-gray.
- Vessels: fine arborizing vessels or hairpin vessels at the edge of the lesion, with no atypical pigment structures.
Clinical Features
- Sex and age: most common in middle-aged men (30–60 years), with a male-to-female ratio of about 3:1.
- Typical sites: over 80% occur on the head and neck, especially the nose, upper lip, cheeks, forehead and ear.
- Appearance: a single firm nodule, slightly mobile under the skin, with a smooth surface and a size of 0.5–3 cm. It grows slowly over years and is neither painful nor itchy.
Multimodal Treatment at Haute-Derma
When treating chondroid syringoma at Haute-Derma, our main goals are to remove the whole tumor including its capsule, prevent recurrence and fully preserve the contours of the face:
Mapping the Margins and Confirming the Diagnosis
- 50 MHz skin ultrasound: assesses depth of invasion and locates the fibrous capsule relative to the facial muscles and superficial vessels.
- Confirmatory biopsy with IHC: staining for PLAG1, CK7, S100, p63 and Ki-67. If Ki-67 is above 10–20% and there is nuclear atypia, management switches immediately to a malignant tumor protocol (malignant chondroid syringoma).
Precise Surgical Excision with Clear (R0) Margins
Complete removal in one piece (en bloc excision): Used for tumors in well-padded areas (cheeks, forehead, chin). The surgeon makes a fine incision along the natural skin tension lines (Langer's lines) and removes the tumor intact with its capsule and a 2–3 mm microscopic safety margin.
Mohs surgery (Mohs micrographic surgery, MMS): Preferred for chondroid syringomas in cosmetically demanding sites (nasal ala, ear rim, columella, nasolabial fold). Because 100% of the surgical margin is checked under the microscope, any small satellite lobules are removed without cutting into the surrounding healthy tissue.
Cosmetic Repair and Aftercare
- Layered cosmetic closure: slowly absorbable 6-0 synthetic sutures for the fascia and subcutaneous layer, with 7-0 monofilament sutures to close the epidermis.
- Exosome / PDRN biological therapy: micro-injections of purified exosomes with PDRN along the wound edges stimulate collagen remodeling and may help shorten healing time.
- Advanced scar therapy: fractional CO2 laser combined with LLLT (633 nm), starting in the third week after surgery, to erase the surgical scar completely.
