The Demise of the Term Bronchioloalveolar Carcinoma Open Access

In the mid-1920s, Edmund Vincent Cowdry, esteemed physician of Cowdry type A and type B inclusion bodies fame, among other entities, published 3 articles about jaagsiekte (from Afrikaans, meaning driving or chasing sickness) and progressive pneumonia in American and South African sheep, in which he described the alveolar thickening and epithelial proliferations typical of jaagsiekte.^1–3  Two decades later, a possible human form of jaagsiekte was reported in the English literature; it was termed alveolar cell carcinoma.^4,5  The tumor, which as it turned out was not human jaagsiekte, was “thought to originate in the lining cells of the alveoli,”^6(p968) distinguishable from other lung cancers “by a regular layer of nonciliated, cuboidal to low columnar cells which line the alveoli, and by the absence of evidence of primary bronchial involvement.”^6(p968) Soon, other diagnostic terms arose within the literature to describe this tumor, including terminal bronchiolar carcinoma, bronchiolar carcinoma, pulmonary adenomatosis, and terminal bronchiolar carcinoma; however, none of them ever became popular.^7–9  The original alveolar cell carcinoma, a descriptively accurate term for the tumor, might have survived,¹⁰  but it also never gained traction. Instead, the diagnostic term bronchioloalveolar carcinoma describing this tumor that has survived for decades originated with the great Avril Liebow.¹¹  He introduced the term as bronchiolo-alveolar carcinoma in 1960, but it had lost its hyphen by the 1970s.^12–15  Bronchioloalveolar carcinoma has remained resilient, despite the occasional publication using one of the older terms and notwithstanding the term's modification to bronchoalveolar carcinoma, an inaccurate but remarkably used term.^16–22  Despite its ease of pronunciation, bronchoalveolar carcinoma should not be used; precision is important in medicine.^23–26 

But now, after decades of beneficial service, the term bronchioloalveolar carcinoma has itself fallen victim to our better understanding of lung cancer. As we have over the decades come to better understand lung neoplasia and preneoplasia, bronchioloalveolar carcinoma (far from being understood as a single, specific lesion as it was originally considered) has leant its appellation to 5 clinically and pathologically distinct entities, namely, 3 nonmucinous lesions (adenocarcinoma in situ, minimally invasive adenocarcinoma, and adenocarcinoma with a prominent lepidic pattern) and 2 mucinous lesions (mucinous adenocarcinoma in situ and mucinous adenocarcinoma). Tangentially, at the most recent biennial meeting of the Pulmonary Pathology Society, discussion regarding the origin of the term lepidic (which refers to neoplastic cells growing along preexisting alveolar structures) concluded that the term is not, as is frequently stated, related to butterflies or other lepidoptera. The term, in fact, is now said to be a neologism, attributed to John George Adami.²⁷ 

With the advancing understanding of lung adenocarcinoma and its precursors, the overly widespread and inappropriate use of the term bronchioloalveolar carcinoma became increasingly recognized, and pulmonary pathologists have acknowledged for several years that “tumors showing a pure bronchioloalveolar or ‘lepidic' pattern are now best regarded as adenocarcinoma-in-situ.”^28(p12) As such, adenocarcinoma in situ, a descriptive and accurate term, has recently been formally proposed as the terminology to be used instead of bronchioloalveolar carcinoma to name pulmonary lesions that are “small (<3 cm), solitary adenocarcinomas with pure lepidic growth”^29(p382) and for which one should expect “100% disease-specific survival if the lesion is completely resected.”^29(p382) In appropriate terminological extension, “small (<3cm), solitary adenocarcinomas with predominant lepidic growth and small foci of invasion measuring 0.5 cm or less”^29(p382) should be termed minimally invasive adenocarcinomas.

With this new terminology come new questions, one of the most important of which is how much invasion qualifies a lesion as minimally invasive adenocarcinoma. Adenocarcinoma in situ and minimally invasive adenocarcinomas are of special interest because of their 100% and near 100% 5-year survival, respectively, if completely resected.³⁰  As Borczuk notes, some criteria are more straightforward than others: “Some criteria are straightforward, such as invasion of the pleura, vessels or airway walls. Once there is confluent scar or desmoplasia in association with glands, this represents invasive adenocarcinoma. If there is a pattern of growth that is a recognized pattern of invasive adenocarcinoma such as acinar, papillary, solid or micropapillary, then this is invasive as well”^{31(pp54–55)} (Figure). Other criteria for diagnosis of minimal invasion are more difficult: “[G]land shapes that are not consistent with alveoli, ie angulated or small nests/glands of tumor cells,”^31(p55) as well as invasive areas that have loss of alveolar macrophages, are helpful, “but this is an inconsistent criterion in practice. Finally, there are often zones of transition from the lepidic pattern to the invasive pattern, and in the zones of transition there is often a change in nuclear grade as well as cellular morphology to a more columnar than cuboidal cell.”^31(p55) It is also important to remember that these terms must be used in their proper context. The terms adenocarcinoma in situ and minimally invasive adenocarcinoma by definition cannot be applied on limited samples such as small biopsies or cytology samples.³² 

The other major group to shed the bronchioloalveolar moniker is the invasive (invasion >5 mm) adenocarcinomas. This group is now categorized based on the individual tumor's predominant histologic pattern, namely, predominant acinar, papillary, solid, micropapillary, or lepidic adenocarcinoma, formerly classified as mixed subtype tumors with nonmucinous bronchioloalveolar pattern.²⁸ The acinar pattern shows glands, round to oval in shape, in a cribriform arrangement, with tumor cells around a central lumen. A solid pattern consists of polygonal tumor cells in sheets in the absence of any of the aforementioned patterns.³³  Papillary architecture consists of columnar cells along central fibrovascular cores. Notably, the micropapillary pattern, associated with a poor prognosis and a higher rate of node metastasis, is characterized by malignant cells growing in micropapillary tufts lacking fibrovascular cores.³⁰  The cells can be detached, connected to alveolar walls, or both, and floating ringlike glandular structures can be seen within the alveolar spaces. The lepidic pattern of growth, with tumor cells growing along preexisting alveolar structures, is characterized by the absence of acinar, solid, papillary, or micropapillary patterns of tumor cell growth. The formerly termed mucinous bronchioloalveolar carcinoma, “characterized by very bland cells with abundant intracytoplasmic mucin, seemingly ‘stuck on' to alveoli with abrupt transitions,”^31(p58) is now termed invasive mucinous adenocarcinoma and is considered an invasive adenocarcinoma rather than an in situ cancer.³⁴ A metastatic mucinous adenocarcinoma from a nonpulmonary primary may be seen lining preexisting alveolar walls and must be distinguished from primary pulmonary mucinous adenocarcina.³⁰ 

Ultimately, examination of the term bronchioloalveolar carcinoma serves as a historical example of the vibrancy of a utile, descriptive term that over time, with increased medical understanding, ran its course and attained obsolescence. It also serves to highlight the potential risk with the advancement of medical understanding of a term being overused to describe too many similar (but ultimately distinct) lesions, from which a term's demise is ultimately derived. Finally, the term may serve as a reminder of the value of using language precisely. At each medical student lecture, it must be reemphasized that the term is bronchioloalveolar carcinoma. It is a linguistic mouthful, and for that reason, too, the term's demise should be respectfully mourned.