Adenocarcinoma with Lepidic Growth(aka BAC and Bronchiocarcinoma)
is a subtype of adenocarcinoma, accounts for about 5% of lung carcinomas but up to 20% are histologically mixed adenocarcinoma and BAC.
It has an indolent course and in its pure form, is really a carcinoma in situ, showing no invasive changes. It does have the potential to evolve into frankly malignant and invasive disease
Smoking appears to some extent be a causative link though it has a disproportionate high incidence among non smokers, women and occurs in a slightly younger population. About 30% of patients with BAC have never smoked. It also has a higher incidence in Japan.
BAC is sometimes associated with patients suffering from interstitial lung disease (eg scleroderma), and also with the uncommon entity of exogenous lipoid pneumonia. .
Structurally, it is characterized by its unique relatively slow lepidic growth, meaning it grows by scaling along the structure of the alveolus or acinus, but does not destroy the architecture. In addition in its pure form it does not invade vascular, lymphatic, or pleural elements.
When it shows invasive properties then it is defined as a mixed BAC adenocarcinoma. Raz There appears to be an evolving spectrum from benign to malignant, starting with premalignant atypical adenomatous hyperplasia, then BAC, and then into a subtype of adenocarcinoma. (Travis)
There is a mucinous form (80%) originating in the mucus secreting columnar cells, and tending to a multicentric pattern. The non mucinous form (20%) arises from the type II pneumocytes of the alveolus, is localized and has a better prognosis.
BAC appears to have characteristic heightened sensitivity to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs).
Clinically, patients in most instances are asymptomatic and many patients are identified by CT screening programs. When the disease is diffuse, bronchorrhea may occur.
The diagnosis is initially suspected radiologically presenting as a solitary ground glass opacity (GG0) (45%), as multicentric nodules (GGOs) (25%), or as a consolidation (30%). Inflammatory or infectious disease is considered in the differential diagnosis, but if the radiologic finding fail to respond to conservative therapy, BAC and its variants become more likely, and surgical biopsy is necessary.
When GGO’s are less than 2cms, they are usually pure BAC. As solid components within the GGO become more apparent, adenocarcinoma becomes more likely. When the disease is multifocal, it defines itself as IIIb or IV
PET scanning has limited sensitivity so that only about 50% of lesions have a diagnostic SUV >2.5
The final diagnosis is made at pathology, and requires histological examination to determine invasion. Cytological aspiration is insufficient.
Treatment depends on staging. When in pure form – as an in situ disease by definition, treatment is surgical and curative. Surgery usually consists of lobar resection, and ipsilateral mediastinal lymphadenectomy. When in the mixed form 10-25% have lymph node involvement and 5% have distant metastases and therefore require additional radiation and chemotherapy.
Pre and Post Op Studies – 79 year old Male with Adenocarcinoma with Lepidic Growth