Apocrine Adenocarcinoma
Primary cutaneous apocrine adenocarcinoma (PCAC) is a rare malignant tumor of the skin adnexa, usually arising from the secretory or ductal part of an apocrine sweat gland. Its biology is complex: it can grow silently in place, recurs often, tends to invade blood and lymphatic vessels (LVI) and may spread to regional lymph nodes early.
Androgen Receptor (AR) and HER2/neu Signaling
- Androgen receptor (AR): like apocrine breast cancer and prostate cancer, PCAC relies heavily on androgen signaling. When androgen binds AR in the nucleus, it switches on genes for apocrine-specific proteins and, by increasing Bcl-2 expression, blocks programmed cell death (apoptosis).
- HER2/neu (ErbB2) overexpression: found in about 30–50% of PCAC cases. HER2 amplification drives the PI3K/AKT/mTOR and MAPK/ERK pathways, promoting distant spread and resistance to conventional chemotherapy.
Decapitation Secretion
- Apocrine differentiation is marked by phospholipid and glycoprotein granules collecting at the top (apex) of the cell.
- As the tumor grows, the cell apex swells and pinches off into the gland lumen (decapitation). Pathologists rely on this sign to recognize apocrine origin.
Histopathology and Immunohistochemistry (IHC) Criteria
Microscopic Features
The tumor usually sits in the deep dermis and subcutaneous fat as a nodule or infiltrative plaque, with these features:
- Tubular, glandular or papillary pattern (tubulopapillary / cribriform): tumor cells form multilayered glands, with papillae projecting into the lumen or sieve-like (cribriform) spaces.
- Apocrine cytology: large polygonal cells with large pale nuclei or prominent nucleoli, and abundant eosinophilic cytoplasm packed with fine granules (resistant to phosphotungstic acid hematoxylin, PTAH).
- Decapitation secretion: visible along the luminal border of well-differentiated cells.
- Grade:
- Well differentiated: clear glandular architecture, obvious cytoplasmic granules, moderate atypia.
- Poorly differentiated: cells grow in solid sheets, with a high nuclear-to-cytoplasmic ratio, many atypical mitoses and central comedonecrosis.
Diagnostic Immunohistochemistry (IHC) Panel
| IHC Marker | Staining Location | Diagnostic Significance |
|---|---|---|
| GCDFP-15 | Tumor cell cytoplasm | STRONGLY POSITIVE (+++); gross cystic disease fluid protein-15, a key marker of apocrine origin |
| Androgen receptor (AR) | Tumor cell nuclei | STRONGLY POSITIVE (+++); confirms apocrine character (>80–90% of cases) |
| Mammaglobin | Cytoplasm | Positive (++); supports apocrine/breast-type glandular differentiation |
| CK7 | Cytoplasm | STRONGLY POSITIVE (+++); cytokeratin marker of glandular epithelium |
| HER2/neu | Cell membrane | Positive (2+/3+) in 30–50% of cases; guides targeted therapy |
| ER / PR | Nuclei | Usually NEGATIVE (unlike typical breast cancer) |
| CK20 / CEA | Cytoplasm | CK20 negative; CEA focally positive along the luminal border |
| p63 / SMA | Myoepithelial cells | Completely LOST around malignant tumor nests (helps separate it from benign tumors) |
Imaging and 50 MHz High-Frequency Ultrasound
- High-frequency skin ultrasound (20–50 MHz):
- A mixed hypoechoic mass containing small anechoic (cyst-like) areas, located deep in the dermis and subcutis.
- Rich blood flow on color Doppler (hypervascularity), with vessels running through the center.
- PET/CT or CT of the chest, abdomen and pelvis: required before treatment to rule out distant metastases and, above all, to exclude breast cancer or eccrine sweat gland carcinoma that has spread to the skin.
Clinical Features
- Typical sites: areas rich in apocrine glands, such as the armpit (>50%), the genital, groin and perianal region, the scalp, the eyelids (glands of Moll) and the outer chest.
- Appearance: a firm lump or nodule under the skin, red-purple, brick-pink or dusky in color; sometimes a hard plaque, or an ulcerated surface that oozes pus or blood.
- Symptoms: usually painless at first, but it can grow quickly and become painful once it invades nerves or becomes infected.
Multimodal Treatment at Haute-Derma
PCAC infiltrates widely and spreads to regional lymph nodes in a high proportion of cases (30–50%). Our standard protocol at Haute-Derma combines microscopic margin control, sentinel lymph node biopsy and targeted systemic therapy:
Biopsy and Full Staging
- Open or core needle biopsy: confirms the diagnosis under the microscope and allows staining for the GCDFP-15 / AR / HER2 / ER / PR / CK7 / p63 panel.
- Whole-body PET/CT: required to exclude a primary breast tumor and to look for nodal or distant spread (lungs, liver, bone).
Mohs Surgery or Wide Excision and Regional Node Management
Controlling the Primary Tumor:
- Mohs micrographic surgery (MMS): the first choice, especially in the armpit, face and genital area, because it spares as much healthy tissue as possible while examining the entire microscopic margin.
- Wide local excision (WLE): when WLE is chosen, margins should be at least 2.0 cm from the tumor edge and include the underlying deep fascia.
Managing Regional Lymph Nodes:
- Sentinel lymph node biopsy (SLNB): indicated for tumors larger than 1.0 cm, with lymphovascular invasion (LVI+), or of high grade (poorly differentiated).
- Regional lymph node dissection: performed when the SLNB is positive or when examination, ultrasound or PET/CT shows nodal metastasis.
Adjuvant Systemic Therapy and Radiotherapy
- Adjuvant radiotherapy:
- Indications: tumors larger than 3–5 cm, close or positive margins that cannot be re-excised, lymphovascular invasion (LVI+) or regional node involvement (N+). Recommended dose: 50–60 Gy to the surgical bed and nodal basin.
- Hormonal anti-androgen therapy:
- Patients with strongly AR-positive (+++) advanced or metastatic disease may respond well to anti-androgens such as enzalutamide or bicalutamide combined with an LHRH agonist.
- HER2-targeted therapy:
- For HER2-overexpressing tumors (IHC 3+ or amplified on FISH), trastuzumab (Herceptin) or pertuzumab may be added to treatment of metastatic or advanced disease.
