Adenocarcinoma in situ, minimally invasive adenocarcinoma and invasive adenocarcinoma of lung

Adenocarcinoma in situ, minimally invasive adenocarcinoma and invasive adenocarcinoma of the lung are relatively new classification entities which replace the now-defunct term bronchoalveolar carcinoma (BAC).

In 2011 the International Association for the Study of Lung Cancer (IASLC) and several other societies jointly revised the classification for adenocarcinoma of lung 13. The new classification strategy is based on a multidisciplinary approach to the diagnosis of lung adenocarcinoma. The terms bronchoalveolar carcinoma and mucinous and non-mucinous bronchoalveolar carcinoma have been rendered obsolete.

Before a general discussion of the topic, it is worth highlighting some of the updated terminology and concepts, as for many who were taught the term bronchoalveolar carcinoma, some adjustment will be necessary 5:

  • adenocarcinoma in situ of lung (AIS) (≤3 cm) has a number of subtypes
    • the most common subtype is non-mucinous and rarely mucinous or mixed subtypes
    • histological pattern: no growth pattern other than lepidic and no feature of necrosis or invasion
  • minimally invasive adenocarcinoma of lung (MIA) ≤3 cm
    • describes small solitary adenocarcinomas with either pure lepidic growth or predominant lepidic growth with ≤5 mm of stromal invasion

The two invasive adenocarcinomas previously termed non-mucinous and mucinous bronchoalveolar carcinoma have been renamed:

AIS and MIA are an uncommon type of bronchial carcinoma which occurs most frequently among non-smokers, women and Asians. It is a subtype of adenocarcinoma, but has a significantly different presentation, treatment and prognosis. Adenocarcinoma in situ and minimally invasive adenocarcinoma represent between 2-14% of all primary pulmonary malignancies 11. There is no significant gender predilection, unlike other lung cancer types which are more prevalent in men.

A focus of pulmonary fibrosis, e.g. tuberculosis scar, infarct, scleroderma.

Presentation is often insidious, and a large proportion (50%) of patients may be asymptomatic at the time of detection 1.  Alternatively, as these tumours can produce large quantities of mucus, patients may present with bronchorrhea.

Persistent consolidation for weeks despite appropriate antimicrobial therapy should raise the suspicion of a neoplastic process. CT or guided biopsy may be planned in such cases.

Adenocarcinoma in situ: ≤3 cm, demonstrates a lepidic growth pattern, spreading along the walls of the lung without destroying the underlying architecture. In addition, they are characterised by the absence of stromal, vascular or pleural invasion.

Minimally invasive adenocarcinoma: ≤3 cm, describes small solitary adenocarcinomas with either pure lepidic growth or predominant lepidic growth with ≤5 mm of stromal invasion.

Three pathological subtypes are recognised 3:

  • non-mucinous
  • mucinous: goblet cell (mucus secreting), often multi-centric
  • mixed

There are three recognised radiographic patterns 1

  • single mass or nodular form (commonest): ~45 %
  • consolidative form: ~30 %
  • multinodular form: ~25 %

May show segmental or lobar consolidation with chronic unilateral airspace opacification and air bronchograms. Can also present as a pulmonary nodule, mass or a cluster of diffuse nodules 1,2. The nodular form (commonest) can be indistinguishable from another adenocarcinoma subtype or inflammatory granuloma on plain film 1.

The appearance of bronchoalveolar carcinoma on CT depends on its pattern of growth; hence, it may appear as:

  • a peripheral nodule
    • commonest appearance
    • typically solitary and well circumscribed 5
    • the nodule may be surrounded by a halo of ground-glass opacity, the so-called fried egg sign
    • cavitation
      • pseudocavitation (presence of bubble-like lucencies) is recognised 1,5
      • overt cavitary changes rarely occur (~7%)
      • cavitating pulmonary metastases may occur (Cheerios sign 9)
  • a focal area of ground glass (early sign)
    • heterogeneous attenuation
  • a region of ground glass, with or without consolidation
  • hilar and mediastinal adenopathy and pleural effusion are uncommon

18F-FDG-PET is often negative 6,7.

Surgical resection is required with a lobectomy or pneumonectomy.

Overall, tumours that demonstrate only lepidic growth tend to be indolent, with a high 5-year survival. However, solid, invasive components are frequently present and despite radical treatment, recurrence rates are high. Mucinous subtypes have worse prognosis 4, probably due to aerogenous spread that forms infiltrating, multifocal, or satellite tumours 11.

The entity formerly known as bronchoalveolar carcinoma was first described by Malassez in 1876, as a bilateral, multinodular form of malignant lung tumour 11-12.

General imaging differential considerations are broad, so it is useful to consider differentials for specific patterns, which include:

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Article information

rID: 5920
Systems: Chest, Oncology
Synonyms or Alternate Spellings:
  • Bronchioloalveolar carcinoma
  • Bronchioloalveolar carcinoma (BAC)
  • Bronchoalveolar carcinoma
  • Bronchioloalveolar cell carcinoma
  • BAC
  • Bronchoalveolar carcinoma (BAC)
  • Adenocarcinoma in situ formally known as bronchoalveolar carcinoma

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Cases and figures

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    Figure 1: histology - with mucin production
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    Figure 2: histology - with mucin production (zoomed)
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    Bronchoalveolar c...
    Case 1
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    Case 2
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    BAC
    Case 3: plain radiograph
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    BAC
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    Bronchoalveolar c...
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    Bronchoalveolar c...
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    Case 5
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    Case 6
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    PA
    Case 7: involving whole lung
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     Case 8
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    Case 9: micronodular form
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